Metal powder for powder metallurgy, compound, granulated powder, and sintered body

ABSTRACT

A metal powder for powder metallurgy according to the invention contains Fe as a principal component, Cr in a proportion of 15 mass % or more and 26 mass % or less, Ni in a proportion of 7 mass % or more and 22 mass % or less, Si in a proportion of 0.3 mass % or more and 1.2 mass % or less, and C in a proportion of 0.005 mass % or more and 0.3 mass % or less, wherein when two elements selected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta are defined as a first element and a second element, the first element is contained in a proportion of 0.01 mass % or more and 0.5 mass % or less and the second element is contained in a proportion of 0.01 mass % or more and 0.5 mass % or less. Further, the metal powder for powder metallurgy preferably has an austenite crystal structure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2015-000678 filed on Jan. 6, 2015. The entire disclosure of JapanesePatent Application No. 2015-000678 is hereby incorporated herein byreference.

BACKGROUND

1. Technical Field

The present invention relates to a metal powder for powder metallurgy, acompound, a granulated powder, and a sintered body.

2. Related Art

In a powder metallurgy method, a composition containing a metal powderand a binder is molded into a desired shape to obtain a molded body, andthe obtained molded body is degreased and sintered, whereby a sinteredbody is produced. In such a process for producing a sintered body, anatomic diffusion phenomenon occurs among particles of the metal powder,whereby the molded body is gradually densified, resulting in sintering.

For example, JP-A-2012-87416 proposes a metal powder for powdermetallurgy which contains Zr and Si, with the remainder including atleast one element selected from the group consisting of Fe, Co, and Ni,and inevitable elements. According to such a metal powder for powdermetallurgy, the sinterability is enhanced by the action of Zr, and asintered body having a high density can be easily produced.

Further, for example, JP-A-6-279913 discloses a composition for metalinjection molding which contains 100 parts by weight of a stainlesssteel powder containing 0.03% by weight or less of C, 8 to 32% by weightof Ni, 12 to 32% by weight of Cr, and 1 to 7% by weight of Mo, with theremainder including Fe and inevitable impurities, and 0.1 to 5.5 partsby weight of at least one powder containing Ti or/and Nb and having anaverage particle diameter of 10 to 60 μm. By using such a compositionobtained by mixing two types of powders, a sintered body having a highsintered density and excellent corrosion resistance is obtained.

Further, for example, JP-A-2007-177675 discloses a needle seal for aneedle valve, which has a composition containing 0.95 to 1.4% by mass ofC, 1.0% by mass or less of Si, 1.0% by mass or less of Mn, 16 to 18% bymass of Cr, and 0.02 to 3% by mass of Nb, with the remainder includingFe and inevitable impurities, has a density after sintering of 7.65 to7.75 g/cm³, and is obtained by molding using a metal injection moldingmethod. According to this, a needle seal having a high density isobtained.

The thus obtained sintered body has become widely used recently for avariety of machine parts, structural parts, and the like.

However, depending on the use of the sintered body, furtherdensification is needed in some cases. In such a case, a sintered bodyis further subjected to an additional treatment such as a hot isostaticpressing treatment (HIP treatment) to increase the density, however, theworkload is significantly increased, and also an increase in the cost isinevitable.

Therefore, an expectation for realization of a metal powder capable ofproducing a sintered body having a high density without performing anadditional treatment or the like has increased.

SUMMARY

An advantage of some aspects of the invention is to provide a metalpowder for powder metallurgy, a compound, and a granulated powder, eachof which is capable of producing a sintered body having a high density,and a sintered body having a high density produced by using the metalpowder for powder metallurgy.

The advantage can be achieved by aspects of the invention describedbelow.

A metal powder for powder metallurgy according to an aspect of theinvention contains Fe as a principal component, Cr in a proportion of15% by mass or more and 26% by mass or less, Ni in a proportion of 7% bymass or more and 22% by mass or less, Si in a proportion of 0.3% by massor more and 1.2% by mass or less, and C in a proportion of 0.005% bymass or more and 0.3% by mass or less, wherein when one element selectedfrom the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta is defined asa first element, and one element selected from the group consisting ofTi, V, Y, Zr, Nb, Hf, and Ta, and having a larger group number in theperiodic table than that of the first element or having the same groupnumber in the periodic table as that of the first element and a largerperiod number in the periodic table than that of the first element isdefined as a second element, the first element is contained in aproportion of 0.01% by mass or more and 0.5% by mass or less, and thesecond element is contained in a proportion of 0.01% by mass or more and0.5% by mass or less.

According to this, the alloy composition is optimized so that thedensification during sintering of the metal powder for powder metallurgycan be enhanced. As a result, a metal powder for powder metallurgycapable of producing a sintered body having a high density is obtainedwithout performing an additional treatment.

In the metal powder for powder metallurgy according to the aspect of theinvention, it is preferred that the metal powder has an austenitecrystal structure.

According to this, high corrosion resistance and large elongation can beprovided to a sintered body to be produced. That is, a metal powder forpowder metallurgy capable of producing a sintered body having highcorrosion resistance and large elongation in spite of a high density isobtained.

In the metal powder for powder metallurgy according to the aspect of theinvention, it is preferred that the ratio (X1/X2) of a value (X1)obtained by dividing the content (E1) of the first element by the massnumber of the first element to a value (X2) obtained by dividing thecontent (E2) of the second element by the mass number of the secondelement is 0.3 or more and 3 or less.

According to this, when the metal powder for powder metallurgy is fired,a difference in timing between the deposition of a carbide or the likeof the first element and the deposition of a carbide or the like of thesecond element can be optimized. As a result, pores remaining in amolded body can be eliminated as if they were swept out sequentiallyfrom the inside, and therefore, pores generated in the sintered body canbe minimized. Accordingly, a metal powder for powder metallurgy capableof producing a sintered body having a high density and excellentsintered body properties is obtained.

In the metal powder for powder metallurgy according to the aspect of theinvention, it is preferred that the sum of the content of the firstelement and the content of the second element is 0.05% by mass or moreand 0.6% by mass or less.

According to this, the densification of a sintered body to be producedbecomes necessary and sufficient.

In the metal powder for powder metallurgy according to the aspect of theinvention, it is preferred that Mo is further contained in a proportionof 1% by mass or more and 5% by mass or less.

According to this, the corrosion resistance of a sintered body to beproduced can be further enhanced without causing a significant decreasein the density of the sintered body.

In the metal powder for powder metallurgy according to the aspect of theinvention, it is preferred that the metal powder has an average particlediameter of 0.5 μm or more and 30 μm or less.

According to this, pores remaining in a sintered body are extremelydecreased, and therefore, a sintered body having a particularly highdensity and particularly excellent mechanical properties can beproduced.

A compound according to an aspect of the invention includes the metalpowder for powder metallurgy according to the aspect of the inventionand a binder which binds the particles of the metal powder for powdermetallurgy to one another.

According to this, a compound capable of producing a sintered bodyhaving a high density is obtained.

A granulated powder according to an aspect of the invention is obtainedby granulating the metal powder for powder metallurgy according to theaspect of the invention.

According to this, a granulated powder capable of producing a sinteredbody having a high density is obtained.

A sintered body according to an aspect of the invention is produced bysintering a metal powder for powder metallurgy containing Fe as aprincipal component, Cr in a proportion of 15% by mass or more and 26%by mass or less, Ni in a proportion of 7% by mass or more and 22% bymass or less, Si in a proportion of 0.3% by mass or more and 1.2% bymass or less, and C in a proportion of 0.005% by mass or more and 0.3%by mass or less, wherein when one element selected from the groupconsisting of Ti, V, Y, Zr, Nb, Hf, and Ta is defined as a firstelement, and one element selected from the group consisting of Ti, V, Y,Zr, Nb, Hf, and Ta, and having a larger group number in the periodictable than that of the first element or having the same group number inthe periodic table as that of the first element and a larger periodnumber in the periodic table than that of the first element is definedas a second element, the first element is contained in a proportion of0.01% by mass or more and 0.5% by mass or less, and the second elementis contained in a proportion of 0.01% by mass or more and 0.5% by massor less.

According to this, a sintered body having a high density is obtainedwithout performing an additional treatment.

In the sintered body according to the aspect of the invention, it ispreferred that a first region which is in the form of a particle and hasa relatively high silicon oxide content and a second region which has arelatively lower silicon oxide content than the first region areincluded.

According to this, the concentration of oxides inside the crystal isdecreased, and also the significant growth of crystal grains issuppressed, and thus, a sintered body having a high density andexcellent mechanical properties is obtained.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, a metal powder for powder metallurgy, a compound, agranulated powder, and a sintered body according to the invention willbe described in detail.

Metal Powder for Powder Metallurgy

First, a metal powder for powder metallurgy according to the inventionwill be described.

In powder metallurgy, a sintered body having a desired shape can beobtained by molding a composition containing a metal powder for powdermetallurgy and a binder into a desired shape, followed by degreasing andsintering. According to such a powder metallurgy technique, an advantagethat a sintered body with a complicated and fine shape can be producedin a near-net shape (a shape close to a final shape) as compared withthe other metallurgy techniques is obtained.

Heretofore, with respect to the metal powder for powder metallurgy to beused in the powder metallurgy, an attempt to increase the density of asintered body to be produced by appropriately changing the compositionthereof has been made. However, in the sintered body, pores are liableto be generated, and therefore, in order to obtain mechanical propertiescomparable to those of ingot materials, it was necessary to furtherincrease the density of the sintered body.

Therefore, in the past, the obtained sintered body was further subjectedto an additional treatment such as a hot isostatic pressing treatment(HIP treatment) to increase the density. However, such an additionaltreatment requires much time, labor and cost, and therefore becomes anobstacle to the expansion of the application of the sintered body.

In consideration of the above-mentioned problems, the present inventorshave made extensive studies to find conditions for obtaining a sinteredbody having a high density without performing an additional treatment.As a result, they found that the density of a sintered body can beincreased by optimizing the composition of an alloy which forms a metalpowder, and thus completed the invention.

Specifically, the metal powder for powder metallurgy according to theinvention is a metal powder which contains Cr in a proportion of 15% bymass or more and 26% by mass or less, Ni in a proportion of 7% by massor more and 22% by mass or less, Si in a proportion of 0.3% by mass ormore and 1.2% by mass or less, C in a proportion of 0.005% by mass ormore and 0.3% by mass or less, the below-mentioned first element in aproportion of 0.01% by mass or more and 0.5% by mass or less, and thebelow-mentioned second element in a proportion of 0.01% by mass or moreand 0.5% by mass or less, with the remainder including Fe and otherelements. According to such a metal powder, as a result of optimizingthe alloy composition, the densification during sintering can beparticularly enhanced. As a result, a sintered body having a highdensity can be produced without performing an additional treatment.

By increasing the density of a sintered body, a sintered body havingexcellent mechanical properties is obtained. Such a sintered body can bewidely applied also to, for example, machine parts, structural parts,and the like, to which an external force (load) is applied.

The first element is one element selected from the group consisting ofthe following seven elements: Ti, V, Y, Zr, Nb, Hf, and Ta, and thesecond element is one element selected from the group consisting of theabove-mentioned seven elements and having a larger group number in theperiodic table than that of the first element or one element selectedfrom the group consisting of the above-mentioned seven elements andhaving the same group number in the periodic table as that of the firstelement and a larger period number in the periodic table than that ofthe first element.

Hereinafter, the alloy composition of the metal powder for powdermetallurgy according to the invention will be described in furtherdetail. In the following description, the “metal powder for powdermetallurgy” is sometimes simply referred to as “metal powder”.

Cr (chromium) is an element which provides corrosion resistance to asintered body to be produced. By using the metal powder containing Cr, asintered body capable of maintaining high mechanical properties over along period of time is obtained.

The content of Cr in the metal powder is set to 15% by mass or more and26% by mass or less, but is preferably 15.5% by mass or more and 25% bymass or less, more preferably 16% by mass or more and 21% by mass orless, further more preferably 16% by mass or more and 20% by mass orless. If the content of Cr is less than the above lower limit, thecorrosion resistance of a sintered body to be produced is insufficientdepending on the overall composition. On the other hand, if the contentof Cr exceeds the above upper limit, the sinterability is deteriorateddepending on the overall composition so that it becomes difficult toincrease the density of the sintered body.

Amore preferred range of the content of Cr is defined according to thecontents of Ni and Mo described below. For example, in the case wherethe content of Ni is 7% by mass or more and 22% by mass or less and thecontent of Mo is less than 1.2% by mass, the content of Cr is morepreferably 18% by mass or more and 20% by mass or less. On the otherhand, in the case where the content of Ni is 10% by mass or more and 22%by mass or less and the content of Mo is 1.2% by mass or more and 5% bymass or less, the content of Cr is more preferably 16% by mass or moreand less than 18% by mass.

Ni is an element which provides corrosion resistance and heat resistanceto a sintered body to be produced as expected.

The content of Ni in the metal powder is preferably set to 7% by mass ormore and 22% by mass or less, more preferably 7.5% by mass or more and17% by mass or less, further more preferably 8% by mass or more and 15%by mass or less. By setting the content of Ni within the above range, asintered body having excellent mechanical properties over a long periodof time can be obtained.

If the content of Ni is less than the above lower limit, the corrosionresistance and the heat resistance of a sintered body to be produced maynot be sufficiently enhanced depending on the overall composition. Onthe other hand, if the content of Ni exceeds the above upper limit, thecorrosion resistance and the heat resistance may be deterioratedinstead.

Si (silicon) is an element which provides corrosion resistance and highmechanical properties to a sintered body to be produced, and by usingthe metal powder containing Si, a sintered body capable of maintaininghigh mechanical properties over a long period of time is obtained.

The content of Si in the metal powder is set to 0.3% by mass or more and1.2% by mass or less, but is preferably 0.4% by mass or more and 1.1% bymass or less, more preferably 0.5% by mass or more and 0.9% by mass orless. If the content of Si is less than the above lower limit, theeffect of the addition of Si is weakened depending on the overallcomposition so that the corrosion resistance and the mechanicalproperties of a sintered body to be produced are deteriorated. On theother hand, if the content of Si exceeds the above upper limit, theamount of Si is too large depending on the overall composition so thatthe corrosion resistance and the mechanical properties are deterioratedinstead.

C (carbon) can particularly enhance the sinterability when it is used incombination with the below-mentioned first element and second element.Specifically, the first element and the second element each form acarbide by binding to C. By dispersedly depositing this carbide, aneffect of preventing the significant growth of crystal grains isexhibited. A clear reason for obtaining such an effect has not beenknown, but one of the reasons therefor is considered to be because thedispersed deposit serves as an obstacle to inhibit the significantgrowth of crystal grains, and therefore, a variation in the size ofcrystal grains is suppressed. Accordingly, it becomes difficult togenerate pores in a sintered body, and also the increase in the size ofcrystal grains is prevented, and thus, a sintered body having a highdensity and excellent mechanical properties is obtained.

The content of C in the metal powder is set to 0.005% by mass or moreand 0.3% by mass or less, but is preferably 0.008% by mass or more and0.15% by mass or less, more preferably 0.01% by mass or more and 0.08%by mass or less. If the content of C is less than the above lower limit,crystal grains are liable to grow depending on the overall compositionso that the mechanical properties of the sintered body are insufficient.On the other hand, if the content of C exceeds the above upper limit,the amount of C is too large depending on the overall composition sothat the sinterability is deteriorated instead.

The first element and the second element each deposit a carbide or anoxide (hereinafter also collectively referred to as “carbide or thelike”). It is considered that this deposited carbide or the likeinhibits the significant growth of crystal grains when the metal powderis sintered. As a result, as described above, it becomes difficult togenerate pores in a sintered body, and also the increase in the size ofcrystal grains is prevented, and thus, a sintered body having a highdensity and excellent mechanical properties is obtained.

In addition, although a detailed description will be given later, thedeposited carbide or the like promotes the accumulation of silicon oxideat a crystal grain boundary, and as a result, the sintering is promotedand the density is increased while preventing the increase in the sizeof crystal grains.

The first element and the second element are two elements selected fromthe group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta, but preferablyinclude an element belonging to group 3A or group 4A in the longperiodic table (Ti, Y, Zr, or Hf). By including an element belonging togroup 3A or group 4A as at least one of the first element and the secondelement, oxygen contained as an oxide in the metal powder is removed andthe sinterability of the metal powder can be particularly enhanced.

The first element is only required to be one element selected from thegroup consisting of Ti, V, Y, Zr, Nb, Hf, and Ta as described above, butis preferably an element belonging to group 3A or group 4A in the longperiodic table in the above-mentioned group. An element belonging togroup 3A or group 4A in the above-mentioned group removes oxygencontained as an oxide in the metal powder and therefore can particularlyenhance the sinterability of the metal powder. According to this, theconcentration of oxygen remaining in the crystal grains after sinteringcan be decreased. As a result, the content of oxygen in the sinteredbody can be decreased, and the density can be increased. Further, theseelements are elements having high activity, and therefore are consideredto cause rapid atomic diffusion. Accordingly, this atomic diffusion actsas a driving force, and thereby a distance between particles of themetal powder is efficiently decreased and a neck is formed between theparticles, so that the densification of a molded body is promoted. As aresult, the density of the sintered body can be further increased.

On the other hand, the second element is only required to be one elementselected from the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta anddifferent from the first element as described above, but is preferablyan element belonging to group 5A in the long periodic table in theabove-mentioned group. An element belonging to group 5A in theabove-mentioned group particularly efficiently deposits theabove-mentioned carbide or the like, and therefore, can efficientlyinhibit the significant growth of crystal grains during sintering. As aresult, the production of fine crystal grains is promoted, and thus, thedensity of the sintered body can be increased and also the mechanicalproperties of the sintered body can be enhanced.

Incidentally, by the combination of the first element with the secondelement composed of the elements as described above, the effects of therespective elements are exhibited without inhibiting each other. Due tothis, the metal powder containing such a first element and a secondelement enables the production of a sintered body having a particularlyhigh density.

More preferably, a combination of an element belonging to group 4A asthe first element with Nb as the second element is adopted.

Further more preferably, a combination of Zr or Hf as the first elementwith Nb as the second element is adopted.

By adopting such a combination, the above-mentioned effect becomes moreprominent.

Among these elements, Zr is a ferrite forming element, and thereforedeposits a body-centered cubic lattice phase. This body-centered cubiclattice phase has more excellent sinterability than the other crystallattice phases, and therefore contributes to the densification of asintered body.

The content of the first element in the metal powder is set to 0.01% bymass or more and 0.5% by mass or less, but is set to preferably 0.03% bymass or more and 0.2% by mass or less, more preferably 0.05% by mass ormore and 0.1% by mass or less. If the content of the first element isless than the above lower limit, the effect of the addition of the firstelement is weakened depending on the overall composition so that thedensity of a sintered body to be produced is not sufficiently increased.On the other hand, if the content of the first element exceeds the aboveupper limit, the amount of the first element is too large depending onthe overall composition so that the ratio of the above-mentioned carbideor the like is too high, and therefore, the densification isdeteriorated instead.

The content of the second element in the metal powder is set to 0.01% bymass or more and 0.5% by mass or less, but is set to preferably 0.03% bymass or more and 0.2% by mass or less, more preferably 0.05% by mass ormore and 0.1% by mass or less. If the content of the second element isless than the above lower limit, the effect of the addition of thesecond element is weakened depending on the overall composition so thatthe density of a sintered body to be produced is not sufficientlyincreased. On the other hand, if the content of the second elementexceeds the above upper limit, the amount of the second element is toolarge depending on the overall composition so that the ratio of theabove-mentioned carbide or the like is too high, and therefore, thedensification is deteriorated instead.

As described above, each of the first element and the second elementdeposits a carbide or the like, however, in the case where an elementbelonging to group 3A or group 4A is selected as the first element asdescribed above and an element belonging to group 5A is selected as thesecond element as described above, it is presumed that when the metalpowder is sintered, the timing when a carbide or the like of the firstelement is deposited and the timing when a carbide or the like of thesecond element is deposited differ from each other. It is consideredthat due to the difference in timing when a carbide or the like isdeposited in this manner, sintering gradually proceeds so that thegeneration of pores is prevented, and thus, a dense sintered body isobtained. That is, it is considered that by the existence of both of thecarbide or the like of the first element and the carbide or the like ofthe second element, the increase in the size of crystal grains can besuppressed while increasing the density of the sintered body.

It is preferred to set the ratio of the content of the first element tothe content of the second element in consideration of the mass number ofthe element selected as the first element and the mass number of theelement selected as the second element.

Specifically, when a value obtained by dividing the content E1 (mass %)of the first element by the mass number of the first element isrepresented by an index X1 and a value obtained by dividing the contentE2 (mass %) of the second element by the mass number of the secondelement is represented by an index X2, the ratio X1/X2 of the index X1to the index X2 is preferably 0.3 or more and 3 or less, more preferably0.5 or more and 2 or less, further more preferably 0.75 or more and 1.3or less. By setting the ratio X1/X2 within the above range, a differencebetween the timing when a carbide or the like of the first element isdeposited and the timing when a carbide or the like of the secondelement is deposited can be optimized. According to this, poresremaining in a molded body can be eliminated as if they were swept outsequentially from the inside, and therefore, pores generated in asintered body can be minimized. Therefore, by setting the ratio X1/X2within the above range, a metal powder capable of producing a sinteredbody having a high density and excellent mechanical properties can beobtained. Further, the balance between the number of atoms of the firstelement and the number of atoms of the second element is optimized, andtherefore, an effect brought about by the first element and an effectbrought about by the second element are synergistically exhibited, andthus, a sintered body having a particularly high density can beobtained.

Here, with respect to a specific example of the combination of the firstelement with the second element, based on the above-mentioned range ofthe ratio X1/X2, the ratio (E1/E2) of the content E1 (mass %) to thecontent E2 (mass %) is also calculated.

For example, in the case where the first element is Zr and the secondelement is Nb, since the mass number of Zr is 91.2 and the mass numberof Nb is 92.9, E1/E2 is preferably 0.29 or more and 2.95 or less, morepreferably 0.49 or more and 1.96 or less.

In the case where the first element is Hf and the second element is Nb,since the mass number of Hf is 178.5 and the mass number of Nb is 92.9,E1/E2 is preferably 0.58 or more and 5.76 or less, more preferably 0.96or more and 3.84 or less.

In the case where the first element is Ti and the second element is Nb,since the mass number of Ti is 47.9 and the mass number of Nb is 92.9,E1/E2 is preferably 0.15 or more and 1.55 or less, more preferably 0.26or more and 1.03 or less.

In the case where the first element is Nb and the second element is Ta,since the mass number of Nb is 92.9 and the mass number of Ta is 180.9,E1/E2 is preferably 0.15 or more and 1.54 or less, more preferably 0.26or more and 1.03 or less.

In the case where the first element is Y and the second element is Nb,since the mass number of Y is 88.9 and the mass number of Nb is 92.9,E1/E2 is preferably 0.29 or more and 2.87 or less, more preferably 0.48or more and 1.91 or less.

In the case where the first element is V and the second element is Nb,since the mass number of V is 50.9 and the mass number of Nb is 92.9,E1/E2 is preferably 0.16 or more and 1.64 or less, more preferably 0.27or more and 1.10 or less.

In the case where the first element is Ti and the second element is Zr,since the mass number of Ti is 47.9 and the mass number of Zr is 91.2,E1/E2 is preferably 0.16 or more and 1.58 or less, more preferably 0.26or more and 1.05 or less.

In the case where the first element is Zr and the second element is Ta,since the mass number of Zr is 91.2 and the mass number of Ta is 180.9,E1/E2 is preferably 0.15 or more and 1.51 or less, more preferably 0.25or more and 1.01 or less.

In the case where the first element is Zr and the second element is V,since the mass number of Zr is 91.2 and the mass number of V is 50.9,E1/E2 is preferably 0.54 or more and 5.38 or less, more preferably 0.90or more and 3.58 or less.

Also in the case of a combination other than the above-mentionedcombinations, E1/E2 can be calculated in the same manner as describedabove.

The sum (E1+E2) of the content E1 of the first element and the contentE2 of the second element is preferably 0.05% by mass or more and 0.6% bymass or less, more preferably 0.10% by mass or more and 0.48% by mass orless, further more preferably 0.12% by mass or more and 0.24% by mass orless. By setting the sum of the content of the first element and thecontent of the second element within the above range, the densificationof a sintered body to be produced becomes necessary and sufficient.

When the ratio of the sum of the content of the first element and thecontent of the second element to the content of Si is represented by(E1+E2)/Si, (E1+E2)/Si is preferably 0.1 or more and 0.7 or less, morepreferably 0.15 or more and 0.6 or less, further more preferably 0.2 ormore and 0.5 or less. By setting the ratio (E1+E2)/Si within the aboverange, a decrease in the toughness or the like when Si is added issufficiently compensated by the addition of the first element and thesecond element. As a result, a metal powder capable of producing asintered body which has excellent mechanical properties such astoughness in spite of a high density and also has excellent corrosionresistance attributed to Si is obtained.

In addition, it is considered that by the addition of appropriateamounts of the first element and the second element, the carbide or thelike of the first element and the carbide or the like of the secondelement act as “nuclei”, and therefore, silicon oxide is accumulated ata crystal grain boundary in the sintered body. By the accumulation ofsilicon oxide at a crystal grain boundary, the concentration of oxidesinside the crystal grain is decreased, and therefore, sintering ispromoted. As a result, it is considered that the densification of thesintered body is further promoted.

The deposited silicon oxide easily moves to the triple point of acrystal grain boundary during the accumulation, and therefore, thecrystal growth is suppressed at this point (a flux pinning effect). As aresult, the significant growth of crystal grains is suppressed, andthus, a sintered body having finer crystals is obtained. Such a sinteredbody has particularly high mechanical properties.

The accumulated silicon oxide is easily located at the triple point of acrystal grain boundary as described above, and therefore tends to beshaped into a particle. Therefore, in the sintered body, a first regionwhich is in the form of such a particle and has a relatively highsilicon oxide content and a second region which has a relatively lowersilicon oxide content than the first region are easily formed. By theexistence of the first region, the concentration of oxides inside thecrystal is decreased, and the significant growth of crystal grains issuppressed as described above.

When a qualitative and quantitative analysis is performed for the firstregion and the second region using an electron beam microanalyzer(EPMA), the first region contains O (oxygen) as a principal element, andthe second region contains Fe as a principal element. As describedabove, the first region mainly exists at a crystal grain boundary, andthe second region mainly exists inside the crystal grain. Therefore, inthe first region, when the sum of the contents of the two elements, Oand Si, and the content of Fe are compared, the sum of the contents ofthe two elements is higher than the content of Fe. On the other hand, inthe second region, the sum of the contents of the two elements, O andSi, is much smaller than the content of Fe. Based on these analysisresults, it is found that Si and O are accumulated in the first region.Specifically, the sum of the content of Si and the content of O ispreferably 1.5 times or more and 10000 times or less the content of Fein the first region. Further, the content of Si in the first region ispreferably 3 times or more and 10000 times or less the content of Si inthe second region.

Further, at least either of the content of the first element and thecontent of the second element satisfies the relationship that thecontent in the first region is larger than the content in the secondregion, which may vary depending on the compositional ratio. Thisindicates that in the first region, the carbide or the like of the firstelement and the carbide or the like of the second element act as nucleiwhen silicon oxide is accumulated as described above. Specifically, thecontent of the first element in the first region is preferably 3 timesor more and 10000 times or less the content of the first element in thesecond region. Similarly, the content of Nb in the first region ispreferably 3 times or more and 10000 times or less the content of Nb inthe second region.

The accumulation of silicon oxide as described above is considered to beone of the causes for the densification of a sintered body. Therefore,it is considered that even in a sintered body having a density increasedaccording to the invention, silicon oxide may not be accumulateddepending on the compositional ratio in some cases.

The diameter of the first region in the form of a particle variesdepending on the content of Si in the entire sintered body, but is setto about 0.5 μm or more and 15 μm or less, preferably about 1 μm or moreand 10 μm or less. According to this, the densification of the sinteredbody can be sufficiently promoted while preventing the decrease in themechanical properties of the sintered body accompanying the accumulationof silicon oxide.

The diameter of the first region can be obtained as the average of thediameter of a circle having the same area (circle equivalent diameter)as that of the first region determined by the color shade in an electronmicrograph of the cross section of the sintered body. When the averageis obtained, the measured values of 10 or more regions are used.

Further, when the ratio of the sum of the content of the first elementand the content of the second element to the content of C is representedby (E1+E2)/C, (E1+E2)/C is preferably 1 or more and 16 or less, morepreferably 2 or more and 13 or less, further more preferably 3 or moreand 10 or less. By setting the ratio (E1+E2)/C within the above range,an increase in the hardness and a decrease in the toughness when C isadded, and an increase in the density brought about by the addition ofthe first element and the second element can be achieved. As a result, ametal powder capable of producing a sintered body which has excellentmechanical properties such as tensile strength and toughness isobtained.

The metal powder is only required to contain two elements selected fromthe group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta, but may furthercontain an element which is selected from this group and is differentfrom these two elements. That is, the metal powder may contain three ormore elements selected from the above-mentioned group. According tothis, the above-mentioned effect can be further enhanced, which slightlyvaries depending on the combination of the elements to be contained.

The metal powder for powder metallurgy according to the invention maycontain, other than these elements, at least one element of Mn, Mo, Cu,N, and S as needed. These elements may be inevitably contained in somecases.

Mn is an element which provides corrosion resistance and high mechanicalproperties to a sintered body to be produced in the same manner as Si.

The content of Mn in the metal powder is not particularly limited, butis preferably 0.01% by mass or more and 3% by mass or less, morepreferably 0.05% by mass or more and 1% by mass or less. By setting thecontent of Mn within the above range, a sintered body having a highdensity and excellent mechanical properties is obtained.

If the content of Mn is less than the above lower limit, the corrosionresistance and the mechanical properties of a sintered body to beproduced may not be sufficiently enhanced depending on the overallcomposition. On the other hand, if the content of Mn exceeds the aboveupper limit, the corrosion resistance and the mechanical properties maybe deteriorated instead.

Mo is an element which enhances the corrosion resistance of a sinteredbody to be produced.

The content of Mo in the metal powder is not particularly limited, butis preferably 1% by mass or more and 5% by mass or less, more preferably1.2% by mass or more and 4% by mass or less, further more preferably 2%by mass or more and 3% by mass or less. By setting the content of Mowithin the above range, the corrosion resistance of a sintered body tobe produced can be further enhanced without causing a large decrease inthe density of the sintered body.

Cu is an element which enhances the corrosion resistance of a sinteredbody to be produced.

The content of Cu in the metal powder is not particularly limited, butis preferably 5% by mass or less, more preferably 1% by mass or more and4% by mass or less. By setting the content of Cu within the above range,the corrosion resistance of a sintered body to be produced can befurther enhanced without causing a large decrease in the density of thesintered body.

N is an element which enhances the mechanical properties such as proofstress of a sintered body to be produced.

The content of N in the metal powder is not particularly limited, but ispreferably 0.03% by mass or more and 1% by mass or less, more preferably0.08% by mass or more and 0.3% by mass or less, further more preferably0.1% by mass or more and 0.25% by mass or less. By setting the contentof N within the above range, the mechanical properties such as proofstress of a sintered body to be produced can be further enhanced withoutcausing a large decrease in the density of the sintered body.

In order to produce the metal powder to which N is added, for example, amethod using a nitrided starting material, a method of introducingnitrogen gas into a molten metal, a method of performing a nitridingtreatment of the produced metal powder, or the like is used.

S is an element which enhances the machinability of a sintered body tobe produced.

The content of S in the metal powder is not particularly limited, but ispreferably 0.5% by mass or less, more preferably 0.01% by mass or moreand 0.3% by mass or less. By setting the content of S within the aboverange, the machinability of a sintered body to be produced can befurther enhanced without causing a large decrease in the density of thesintered body.

To the metal powder for powder metallurgy according to the invention, W,Co, B, Se, Te, Pd, Al, or the like may be added other than theabove-mentioned elements. At this time, the contents of these elementsare not particularly limited, but the content of each of these elementsis preferably less than 0.1% by mass, and also the total content ofthese elements is preferably less than 0.2% by mass. These elements maybe inevitably contained in some cases.

The metal powder for powder metallurgy according to the invention maycontain impurities. Examples of the impurities include all elementsother than the above-mentioned elements, and specific examples thereofinclude Li, Be, Na, Mg, P, K, Ca, Sc, Zn, Ga, Ge, Ag, In, Sn, Sb, Os,Ir, Pt, Au, and Bi. The incorporation amount of these impurity elementsis preferably set such that the content of each of the impurity elementsis less than the content of each of Fe, Cr, Ni, Si, the first element,and the second element. Further, the incorporation amounts of theseimpurity elements are preferably set such that the content of each ofthe impurity elements is less than 0.03% by mass, more preferably lessthan 0.02% by mass. Further, the total content of these impurityelements is set to preferably less than 0.3% by mass, more preferablyless than 0.2% by mass. These elements do not inhibit the effect asdescribed above as long as the content thereof is within the aboverange, and therefore may be intentionally added to the metal powder.

Meanwhile, O (oxygen) may also be intentionally added to or inevitablymixed in the metal powder, however, the amount thereof is preferablyabout 0.8% by mass or less, more preferably about 0.5% by mass or less.By controlling the amount of oxygen in the metal powder within the aboverange, the sinterability is enhanced, and thus, a sintered body having ahigh density and excellent mechanical properties is obtained.Incidentally, the lower limit thereof is not particularly set, but ispreferably 0.03% by mass or more from the viewpoint of ease of massproduction or the like.

Fe is a component (principal component) whose content is the highest inthe alloy constituting the metal powder for powder metallurgy accordingto the invention and has a great influence on the properties of thesintered body. The content of Fe is not particularly limited, but ispreferably 50% by mass or more.

The compositional ratio of the metal powder for powder metallurgy can bedetermined by, for example, Iron and steel—Atomic absorptionspectrometric method specified in JIS G 1257 (2000), Iron and steel—ICPatomic emission spectrometric method specified in JIS G 1258 (2007),Iron and steel—Method for spark discharge atomic emission spectrometricanalysis specified in JIS G 1253 (2002), Iron and steel—Method for X-rayfluorescence spectrometric analysis specified in JIS G 1256 (1997),gravimetric, titrimetric, and absorption spectrometric methods specifiedin JIS G 1211 to G 1237, or the like. Specifically, for example, anoptical emission spectrometer for solids (spark optical emissionspectrometer, model: SPECTROLAB, type: LAVMB08A) manufactured by SPECTROAnalytical Instruments GmbH or an ICP device (model: CIROS-120)manufactured by Rigaku Corporation can be used.

Incidentally, the methods specified in JIS G 1211 to G 1237 are asfollows.

JIS G 1211 (2011): Iron and steel—Methods for determination of carboncontent

JIS G 1212 (1997): Iron and steel—Methods for determination of siliconcontent

JIS G 1213 (2001): Iron and steel—Methods for determination of manganesecontent

JIS G 1214 (1998): Iron and steel—Methods for determination ofphosphorus content

JIS G 1215 (2010): Iron and steel—Methods for determination of sulfurcontent

JIS G 1216 (1997): Iron and steel—Methods for determination of nickelcontent

JIS G 1217 (2005): Iron and steel—Methods for determination of chromiumcontent

JIS G 1218 (1999): Iron and steel—Methods for determination ofmolybdenum content

JIS G 1219 (1997): Iron and steel—Methods for determination of coppercontent

JIS G 1220 (1994): Iron and steel—Methods for determination of tungstencontent

JIS G 1221 (1998): Iron and steel—Methods for determination of vanadiumcontent

JIS G 1222 (1999): Iron and steel—Methods for determination of cobaltcontent

JIS G 1223 (1997): Iron and steel—Methods for determination of titaniumcontent

JIS G 1224 (2001): Iron and steel—Methods for determination of aluminumcontent

JIS G 1225 (2006): Iron and steel—Methods for determination of arseniccontent

JIS G 1226 (1994): Iron and steel—Methods for determination of tincontent

JIS G 1227 (1999): Iron and steel—Methods for determination of boroncontent

JIS G 1228 (2006): Iron and steel—Methods for determination of nitrogencontent

JIS G 1229 (1994): Steel—Methods for determination of lead content

JIS G 1232 (1980): Methods for determination of zirconium in steel

JIS G 1233 (1994): Steel—Method for determination of selenium content

JIS G 1234 (1981): Methods for determination of tellurium in steel

JIS G 1235 (1981): Methods for determination of antimony in iron andsteel

JIS G 1236 (1992): Method for determination of tantalum in steel

JIS G 1237 (1997): Iron and steel—Methods for determination of niobiumcontent

Further, when C (carbon) and S (sulfur) are determined, particularly, aninfrared absorption method after combustion in a current of oxygen(after combustion in a high-frequency induction heating furnace)specified in JIS G 1211 (2011) is also used. Specifically, acarbon-sulfur analyzer, CS-200 manufactured by LECO Corporation can beused.

Further, when N (nitrogen) and O (oxygen) are determined, particularly,a method for determination of nitrogen content in iron and steelspecified in JIS G 1228 (2006) and a method for determination of oxygencontent in metallic materials specified in JIS Z 2613 (2006) are alsoused. Specifically, an oxygen-nitrogen analyzer, TC-300/EF-300manufactured by LECO Corporation can be used.

The metal powder for powder metallurgy according to the inventionpreferably has an austenite crystal structure. The austenite crystalstructure provides high corrosion resistance and also large elongationto a sintered body. Due to this, the metal powder for powder metallurgyhaving such a crystal structure is capable of producing a sintered bodyhaving high corrosion resistance and large elongation in spite of a highdensity.

It can be determined whether or not the metal powder for powdermetallurgy has an austenite crystal structure by, for example, X-raydiffractometry.

The average particle diameter of the metal powder for powder metallurgyaccording to the invention is preferably 0.5 μm or more and 30 μm orless, more preferably 1 μm or more and 20 μm or less, further morepreferably 2 μm or more and 10 μm or less. By using the metal powder forpowder metallurgy having such a particle diameter, pores remaining in asintered body are extremely reduced, and therefore, a sintered bodyhaving a particularly high density and particularly excellent mechanicalproperties can be produced.

The average particle diameter can be obtained as a particle diameterwhen the cumulative amount obtained by cumulating the percentages of theparticles from the smaller diameter side reaches 50% in a cumulativeparticle size distribution on a mass basis obtained by laserdiffractometry.

If the average particle diameter of the metal powder for powdermetallurgy is less than the above lower limit, the moldability isdeteriorated in the case where the shape which is difficult to mold isformed, and therefore, the sintered density may be decreased. On theother hand, if the average particle diameter of the metal powder exceedsthe above upper limit, spaces between the particles become larger duringmolding, and therefore, the sintered density may be decreased also inthis case.

The particle size distribution of the metal powder for powder metallurgyis preferably as narrow as possible. Specifically, when the averageparticle diameter of the metal powder for powder metallurgy is withinthe above range, the maximum particle diameter of the metal powder ispreferably 200 μm or less, more preferably 150 μm or less. Bycontrolling the maximum particle diameter of the metal powder for powdermetallurgy within the above range, the particle size distribution of themetal powder for powder metallurgy can be made narrower, and thus, thedensity of the sintered body can be further increased.

Here, the “maximum particle diameter” refers to a particle diameter whenthe cumulative amount obtained by cumulating the percentages of theparticles from the smaller diameter side reaches 99.9% in a cumulativeparticle size distribution on amass basis obtained by laserdiffractometry.

When the minor axis of each particle of the metal powder for powdermetallurgy is represented by S (μm) and the major axis thereof isrepresented by L (μm), the average of the aspect ratio defined by S/L ispreferably about 0.4 or more and 1 or less, more preferably about 0.7 ormore and 1 or less. The metal powder for powder metallurgy having anaspect ratio within this range has a shape relatively close to aspherical shape, and therefore, the packing factor when the metal powderis molded is increased. As a result, the density of the sintered bodycan be further increased.

Here, the “major axis” is the maximum length in the projected image ofthe particle, and the “minor axis” is the maximum length in thedirection perpendicular to the major axis. Incidentally, the average ofthe aspect ratio can be obtained as the average of the measured aspectratios of 100 or more particles.

The tap density of the metal powder for powder metallurgy according tothe invention is preferably 3.5 g/cm³ or more, more preferably 4 g/cm³or more. According to the metal powder for powder metallurgy having sucha high tap density, when a molded body is obtained, the interparticlepacking efficiency is particularly increased. Therefore, a particularlydense sintered body can be obtained in the end.

The specific surface area of the metal powder for powder metallurgyaccording to the invention is not particularly limited, but ispreferably 0.1 m²/g or more, more preferably 0.2 m²/g or more. Accordingto the metal powder for powder metallurgy having such a large specificsurface area, a surface activity (surface energy) is increased so thatit is possible to easily sinter the metal powder even if less energy isapplied. Therefore, when a molded body is sintered, a difference insintering rate hardly occurs between the inner side and the outer sideof the molded body, and thus, the decrease in the sintered density dueto the pores remaining inside the molded body can be suppressed.

Method for Producing Sintered Body

Next, a method for producing a sintered body using such a metal powderfor powder metallurgy according to the invention will be described.

The method for producing a sintered body includes (A) a compositionpreparation step in which a composition for producing a sintered body isprepared, (B) a molding step in which a molded body is produced, (C) adegreasing step in which a degreasing treatment is performed, and (D) afiring step in which firing is performed. Hereinafter, the respectivesteps will be described sequentially.

(A) Composition Preparation Step

First, the metal powder for powder metallurgy according to the inventionand a binder are prepared, and these materials are kneaded using akneader, whereby a kneaded material is obtained.

In this kneaded material (an embodiment of the compound according to theinvention), the metal powder for powder metallurgy is uniformlydispersed.

The metal powder for powder metallurgy according to the invention isproduced by, for example, any of a variety of powdering methods such asan atomization method (such as a water atomization method, a gasatomization method, or a spinning water atomization method), a reducingmethod, a carbonyl method, and a pulverization method.

Among these, the metal powder for powder metallurgy according to theinvention is preferably a metal powder produced by an atomizationmethod, more preferably a metal powder produced by a water atomizationmethod or a spinning water atomization method. The atomization method isa method in which a molten metal (metal melt) is caused to collide witha fluid (liquid or gas) sprayed at a high speed to atomize the metalmelt into a fine powder and also to cool the fine powder, whereby ametal powder is produced. By producing the metal powder for powdermetallurgy through such an atomization method, an extremely fine powdercan be efficiently produced. Further, the shape of the particle of theobtained powder is closer to a spherical shape by the action of surfacetension. Due to this, when the metal powder is molded, a molded bodyhaving a high packing factor is obtained. That is, a powder capable ofproducing a sintered body having a high density can be obtained.

In the case where a water atomization method is used as the atomizationmethod, the pressure of water (hereinafter referred to as “atomizationwater”) to be sprayed to the molten metal is not particularly limited,but is set to preferably about 75 MPa or more and 120 MPa or less (750kgf/cm² or more and 1200 kgf/cm² or less), more preferably about 90 MPaor more and 120 MPa or less (900 kgf/cm² or more and 1200 kgf/cm² orless).

The temperature of the atomization water is also not particularlylimited, but is preferably set to about 1° C. or higher and 20° C. orlower.

The atomization water is often sprayed in a cone shape such that it hasa vertex on the falling path of the metal melt and the outer diametergradually decreases downward. In this case, the vertex angle θ of thecone formed by the atomization water is preferably about 10° or more and40° or less, more preferably about 15° or more and 35° or less.According to this, a metal powder for powder metallurgy having acomposition as described above can be reliably produced.

Further, by using a water atomization method (particularly, a spinningwater atomization method), the metal melt can be cooled particularlyquickly. Due to this, a powder having high quality can be obtained in awide alloy composition range.

The cooling rate when cooling the metal melt in the atomization methodis preferably 1×10⁴° C./s or more, more preferably 1×10⁵° C./s or more.By the quick cooling in this manner, a homogeneous metal powder forpowder metallurgy can be obtained. As a result, a sintered body havinghigh quality can be obtained.

The thus obtained metal powder for powder metallurgy may be classifiedas needed. Examples of the classification method include dryclassification such as sieving classification, inertial classification,and centrifugal classification, and wet classification such assedimentation classification.

Examples of the binder include polyolefins such as polyethylene,polypropylene, and ethylene-vinyl acetate copolymers, acrylic resinssuch as polymethyl methacrylate and polybutyl methacrylate, styrenicresins such as polystyrene, polyesters such as polyvinyl chloride,polyvinylidene chloride, polyamide, polyethylene terephthalate, andpolybutylene terephthalate, various resins such as polyether, polyvinylalcohol, polyvinylpyrrolidone, and copolymers thereof, and variousorganic binders such as various waxes, paraffins, higher fatty acids(such as stearic acid), higher alcohols, higher fatty acid esters, andhigher fatty acid amides. These can be used alone or by mixing two ormore types thereof.

The content of the binder is preferably about 2% by mass or more and 20%by mass or less, more preferably about 5% by mass or more and 10% bymass or less with respect to the total amount of the kneaded material.By setting the content of the binder within the above range, a moldedbody can be formed with good moldability, and also the density isincreased, whereby the stability of the shape of the molded body and thelike can be particularly enhanced. Further, according to this, adifference in size between the molded body and the degreased body, thatis, so-called a shrinkage ratio is optimized, whereby a decrease in thedimensional accuracy of the finally obtained sintered body can beprevented. That is, a sintered body having a high density and highdimensional accuracy can be obtained.

In the kneaded material, a plasticizer may be added as needed. Examplesof the plasticizer include phthalate esters (such as DOP, DEP, and DBP),adipate esters, trimellitate esters, and sebacate esters. These can beused alone or by mixing two or more types thereof.

Further, in the kneaded material, other than the metal powder for powdermetallurgy, the binder, and the plasticizer, for example, any of avariety of additives such as a lubricant, an antioxidant, a degreasingaccelerator, and a surfactant can be added as needed.

The kneading conditions vary depending on the respective conditions suchas the metal composition or the particle diameter of the metal powderfor powder metallurgy to be used, the composition of the binder, and theblending amount thereof. However, for example, the kneading temperaturecan be set to about 50° C. or higher and 200° C. or lower, and thekneading time can be set to about 15 minutes or more and 210 minutes orless.

Further, the kneaded material is formed into a pellet (small particle)as needed. The particle diameter of the pellet is set to, for example,about 1 mm or more and 15 mm or less.

Incidentally, depending on the molding method described below, in placeof the kneaded material, a granulated powder may be produced. Thekneaded material, the granulated powder, and the like are examples ofthe composition to be subjected to the molding step described below.

The embodiment of the granulated powder according to the invention isdirected to a granulated powder obtained by binding a plurality of metalparticles to one another with a binder by subjecting the metal powderfor powder metallurgy according to the invention to a granulationtreatment.

Examples of the binder to be used for producing the granulated powderinclude polyolefins such as polyethylene, polypropylene, andethylene-vinyl acetate copolymers, acrylic resins such as polymethylmethacrylate and polybutyl methacrylate, styrenic resins such aspolystyrene, polyesters such as polyvinyl chloride, polyvinylidenechloride, polyamide, polyethylene terephthalate, and polybutyleneterephthalate, various resins such as polyether, polyvinyl alcohol,polyvinylpyrrolidone, and copolymers thereof, and various organicbinders such as various waxes, paraffins, higher fatty acids (such asstearic acid), higher alcohols, higher fatty acid esters, and higherfatty acid amides. These can be used alone or by mixing two or moretypes thereof.

Among these, as the binder, a binder containing a polyvinyl alcohol orpolyvinylpyrrolidone is preferred. These binder components have a highbinding ability, and therefore can efficiently form the granulatedpowder even in a relatively small amount. Further, the thermaldecomposability thereof is also high, and therefore, the binder can bereliably decomposed and removed in a short time during degreasing andfiring.

The content of the binder is preferably about 0.2% by mass or more and10% by mass or less, more preferably about 0.3% by mass or more and 5%by mass or less, further more preferably about 0.3% by mass or more and2% by mass or less with respect to the total amount of the granulatedpowder. By setting the content of the binder within the above range, thegranulated powder can be efficiently formed while preventingsignificantly large particles from being formed or the metal particleswhich are not granulated from remaining in a large amount. Further,since the moldability is improved, the stability of the shape of themolded body and the like can be particularly enhanced. Further, bysetting the content of the binder within the above range, a differencein size between the molded body and the degreased body, that is,so-called a shrinkage ratio is optimized, whereby a decrease in thedimensional accuracy of the finally obtained sintered body can beprevented.

Further, in the granulated powder, any of a variety of additives such asa plasticizer, a lubricant, an antioxidant, a degreasing accelerator,and a surfactant may be added as needed.

Examples of the granulation treatment include a spray drying method, atumbling granulation method, a fluidized bed granulation method, and atumbling fluidized bed granulation method.

In the granulation treatment, a solvent which dissolves the binder isused as needed. Examples of the solvent include inorganic solvents suchas water and carbon tetrachloride, and organic solvents such asketone-based solvents, alcohol-based solvents, ether-based solvents,cellosolve-based solvents, aliphatic hydrocarbon-based solvents,aromatic hydrocarbon-based solvents, aromatic heterocycliccompound-based solvents, amide-based solvents, halogen compound-basedsolvents, ester-based solvents, amine-based solvents, nitrile-basedsolvents, nitro-based solvents, and aldehyde-based solvents, and onetype or a mixture of two or more types selected from these solvents isused.

The average particle diameter of the granulated powder is notparticularly limited, and is preferably about 10 μm or more and 200 μmor less, more preferably about 20 μm or more and 100 μm or less, furthermore preferably about 25 μm or more and 60 μm or less. The granulatedpowder having such a particle diameter has favorable fluidity, and canmore faithfully reflect the shape of a molding die.

The average particle diameter can be obtained as a particle diameterwhen the cumulative amount obtained by cumulating the percentages of theparticles from the smaller diameter side reaches 50% in a cumulativeparticle size distribution on amass basis obtained by laserdiffractometry.

(B) Molding Step

Subsequently, the kneaded material or the granulated powder is molded,whereby a molded body having the same shape as that of a desiredsintered body is produced.

The method for producing a molded body (molding method) is notparticularly limited, and for example, any of a variety of moldingmethods such as a powder compacting (compression molding) method, ametal powder injection molding (MIM: Metal Injection Molding) method,and an extrusion molding method can be used.

The molding conditions in the case of a powder compacting method amongthese methods are preferably such that the molding pressure is about 200MPa or more and 1000 MPa or less (2 t/cm² or more and 10 t/cm² or less),which vary depending on the respective conditions such as thecomposition and the particle diameter of the metal powder for powdermetallurgy to be used, the composition of the binder, and the blendingamount thereof.

The molding conditions in the case of a metal powder injection moldingmethod are preferably such that the material temperature is about 80° C.or higher and 210° C. or lower, and the injection pressure is about 50MPa or more and 500 MPa or less (0.5 t/cm² or more and 5 t/cm² or less),which vary depending on the respective conditions.

The molding conditions in the case of an extrusion molding method arepreferably such that the material temperature is about 80° C. or higherand 210° C. or lower, and the extrusion pressure is about 50 MPa or moreand 500 MPa or less (0.5 t/cm² or more and 5 t/cm² or less), which varydepending on the respective conditions.

The thus obtained molded body is in a state where the binder isuniformly distributed in spaces between the particles of the metalpowder.

The shape and size of the molded body to be produced are determined inanticipation of shrinkage of the molded body in the subsequentdegreasing step and firing step.

(C) Degreasing Step

Subsequently, the thus obtained molded body is subjected to a degreasingtreatment (binder removal treatment), whereby a degreased body isobtained.

Specifically, the binder is decomposed by heating the molded body,whereby the binder is removed from the molded body. In this manner, thedegreasing treatment is performed.

Examples of the degreasing treatment include a method of heating themolded body and a method of exposing the molded body to a gas capable ofdecomposing the binder.

In the case of using a method of heating the molded body, the conditionsfor heating the molded body are preferably such that the temperature isabout 100° C. or higher and 750° C. or lower and the time is about 0.1hours or more and 20 hours or less, and more preferably such that thetemperature is about 150° C. or higher and 600° C. or lower and the timeis about 0.5 hours or more and 15 hours or less, which slightly varydepending on the composition and the blending amount of the binder.According to this, the degreasing of the molded body can be necessarilyand sufficiently performed without sintering the molded body. As aresult, it is possible to reliably prevent the binder component fromremaining inside the degreased body in a large amount.

The atmosphere when the molded body is heated is not particularlylimited, and an atmosphere of a reducing gas such as hydrogen, anatmosphere of an inert gas such as nitrogen or argon, an atmosphere ofan oxidative gas such as air, a reduced pressure atmosphere obtained byreducing the pressure of such an atmosphere, or the like can be used.

Examples of the gas capable of decomposing the binder include ozone gas.

Incidentally, by dividing this degreasing step into a plurality of stepsin which the degreasing conditions are different, and performing theplurality of steps, the binder in the molded body can be more rapidlydecomposed and removed so that the binder does not remain in the moldedbody.

Further, according to need, the degreased body may be subjected to amachining process such as grinding, polishing, or cutting. The degreasedbody has a relatively low hardness and relatively high plasticity, andtherefore, the machining process can be easily performed whilepreventing the degreased body from losing its shape. According to such amachining process, a sintered body having high dimensional accuracy canbe easily obtained in the end.

(D) Firing Step

The degreased body obtained in the above step (C) is fired in a firingfurnace, whereby a sintered body is obtained.

By this firing, in the metal powder for powder metallurgy, diffusionoccurs at the boundary surface between the particles, resulting insintering. At this time, by the mechanism as described above, thedegreased body is rapidly sintered. As a result, a sintered body whichis dense and has a high density on the whole is obtained.

The firing temperature varies depending on the composition, the particlediameter, and the like of the metal powder for powder metallurgy used inthe production of the molded body and the degreased body, but is set to,for example, about 980° C. or higher and 1330° C. or lower, andpreferably set to about 1050° C. or higher and 1260° C. or lower.

Further, the firing time is set to 0.2 hours or more and 7 hours orless, but is preferably set to about 1 hour or more and 6 hours or less.

In the firing step, the firing temperature or the below-described firingatmosphere may be changed in the middle of the step.

By setting the firing conditions within such a range, it is possible tosufficiently sinter the entire degreased body while preventing thesintering from proceeding excessively to cause oversintering andincrease the size of the crystal structure. As a result, a sintered bodyhaving a high density and particularly excellent mechanical propertiescan be obtained.

Further, since the firing temperature is a relatively low temperature,it is easy to control the heating temperature in the firing furnace tobe constant, and therefore, it is also easy to maintain the temperatureof the degreased body constant. As a result, a more homogeneous sinteredbody can be produced.

Further, since the firing temperature as described above is atemperature which can be sufficiently realized using a common firingfurnace, and therefore, an inexpensive firing furnace can be used, andalso the running cost can be kept low. In other words, in the case wherethe temperature exceeds the above-mentioned firing temperature, it isnecessary to employ an expensive firing furnace using a special heatresistant material, and also the running cost may be increased.

The atmosphere when performing firing is not particularly limited,however, in consideration of prevention of significant oxidation of themetal powder, an atmosphere of a reducing gas such as hydrogen, anatmosphere of an inert gas such as argon, a reduced pressure atmosphereobtained by reducing the pressure of such an atmosphere, or the like ispreferably used.

The thus obtained sintered body has a high density and excellentmechanical properties. That is, a sintered body produced by molding acomposition containing the metal powder for powder metallurgy accordingto the invention and a binder, followed by degreasing and sintering hasa higher relative density than a sintered body obtained by sintering ametal powder in the related art. Therefore, according to the invention,a sintered body having a high density which could not be obtained unlessan additional treatment such as an HIP treatment is performed can berealized without performing an additional treatment.

Specifically, according to the invention, for example, the relativedensity can be expected to be increased by 2% or more as compared withthe related art, which slightly varies depending on the composition ofthe metal powder for powder metallurgy.

As a result, the relative density of the obtained sintered body can beexpected to be, for example, 97% or more (preferably 98% or more, morepreferably 98.5% or more). The sintered body having a relative densitywithin such a range has excellent mechanical properties comparable tothose of ingot materials although it has a shape as close as possible toa desired shape by using a powder metallurgy technique, and therefore,the sintered body can be applied to a variety of machine parts,structural parts, and the like with virtually no post-processing.

Further, the tensile strength and the 0.2% proof stress of a sinteredbody produced by molding a composition containing the metal powder forpowder metallurgy according to the invention and a binder, followed bydegreasing and sintering are higher than those of a sintered bodyobtained by performing sintering in the same manner using a metal powderin the related art. This is considered to be because by optimizing thealloy composition, the sinterability of the metal powder is enhanced,and thus, the mechanical properties of a sintered body to be producedusing the metal powder are enhanced.

Further, the sintered body produced as described above has a highsurface hardness. Specifically, as one example, the Vickers hardness ofthe surface of the sintered body is expected to be 140 or more and 500or less, which slightly varies depending on the composition of the metalpowder for powder metallurgy, and further is expected to be preferably150 or more and 400 or less. The sintered body having such a hardnesshas particularly high durability.

The sintered body has a sufficiently high density and mechanicalproperties even without performing an additional treatment, however, inorder to further increase the density and enhance the mechanicalproperties, a variety of additional treatments may be performed.

As the additional treatment, for example, an additional treatment ofincreasing the density such as the HIP treatment described above may beperformed, and also a variety of quenching treatments, a variety ofsub-zero treatments, a variety of tempering treatments, and the like maybe performed. These additional treatments may be performed alone or twoor more treatments thereof may be performed in combination.

In the firing step and a variety of additional treatments describedabove, a light element in the metal powder (in the sintered body) isvolatilized, and the composition of the finally obtained sintered bodyslightly changes from the composition of the metal powder in some cases.

For example, the content of C in the final sintered body may changewithin the range of 5% or more and 100% or less (preferably within therange of 30% or more and 100% or less) of the content of C in the metalpowder for powder metallurgy, which varies depending on the conditionsfor the step or the conditions for the treatment.

Also the content of O in the final sintered body may change within therange of 1% or more and 50% or less (preferably within the range of 3%or more and 50% or less) of the content of O in the metal powder forpowder metallurgy, which varies depending on the conditions for the stepor the conditions for the treatment.

On the other hand, as described above, the produced sintered body may besubjected to an HIP treatment as part of the additional treatments to beperformed as needed, however, even if the HIP treatment is performed, asufficient effect is not exhibited in many cases. In the HIP treatment,the density of the sintered body can be further increased, however, thedensity of the sintered body obtained according to the invention hasalready been sufficiently increased at the end of the firing step in thefirst place. Therefore, even if the HIP treatment is further performed,densification hardly proceeds any further.

In addition, in the HIP treatment, it is necessary to apply pressure toa material to be treated through a pressure medium, and therefore, thematerial to be treated may be contaminated, the composition or thephysical properties of the material to be treated may unintentionallychange accompanying the contamination, or the color of the material tobe treated may change accompanying the contamination. Further, by theapplication of pressure, residual stress is generated or increased inthe material to be treated, and a problem such as a change in the shapeor a decrease in the dimensional accuracy may occur as the residualstress is released over time.

On the other hand, according to the invention, a sintered body having asufficiently high density can be produced without performing such an HIPtreatment, and therefore, a sintered body having an increased densityand also an increased strength can be obtained in the same manner as inthe case of performing an HIP treatment. Such a sintered body is lesscontaminated and discolored, and also an unintended change in thecomposition or physical properties, or the like occurs less, and also aproblem such as a change in the shape or a decrease in the dimensionalaccuracy occurs less. Therefore, according to the invention, a sinteredbody having high mechanical strength and dimensional accuracy, andexcellent durability can be efficiently produced.

Further, the sintered body produced according to the invention requiresalmost no additional treatments for enhancing the mechanical properties,and therefore, the composition and the crystal structure tend to becomeuniform in the entire sintered body. Due to this, the sintered body hashigh structural anisotropy and therefore has excellent durabilityagainst a load from every direction regardless of its shape.

Incidentally, it is confirmed that in the thus produced sintered body,the porosity near the surface thereof is often relatively smaller thaninside the sintered body. The reason therefor is not clear, however, oneof the reasons is that by the addition of the first element and thesecond element, the sintering reaction more easily proceeds near thesurface of the molded body than inside the molded body.

Specifically, when the porosity near the surface of the sintered body isrepresented by A1 and the porosity inside the sintered body isrepresented by A2, A2−A1 is preferably 0.1% or more and 3% or less, morepreferably 0.2% or more and 2% or less. The sintered body showing thevalue of A2−A1 within the above range not only has necessary andsufficient mechanical strength, but also can easily flatten the surface.That is, by polishing the surface of such a sintered body, a surfacehaving high specularity can be obtained.

Such a sintered body having high specularity not only has highmechanical strength, but also has excellent aesthetic properties.Therefore, such a sintered body is favorably used also for applicationrequiring excellent aesthetic appearance.

Incidentally, the porosity A1 near the surface of the sintered bodyrefers to a porosity in a 25-μm radius region centered on the positionat a depth of 50 μm from the surface of the cross section of thesintered body. Further, the porosity A2 inside the sintered body refersto a porosity in a 25-μm radius region centered on the position at adepth of 300 μm from the surface of the cross section of the sinteredbody. These porosities are values obtained by observing the crosssection of the sintered body with a scanning electron microscope anddividing the area of pores present in the region by the area of theregion.

Hereinabove, the metal powder for powder metallurgy, the compound, thegranulated powder, and the sintered body according to the invention havebeen described with reference to preferred embodiments, however, theinvention is not limited thereto.

Further, the sintered body according to the invention is used for, forexample, parts for transport machinery such as parts for automobiles,parts for bicycles, parts for railcars, parts for ships, parts forairplanes, and parts for space transport machinery (such as rockets);parts for electronic devices such as parts for personal computers andparts for mobile phone terminals; parts for electrical devices such asrefrigerators, washing machines, and cooling and heating machines; partsfor machines such as machine tools and semiconductor production devices;parts for plants such as atomic power plants, thermal power plants,hydroelectric power plants, oil refinery plants, and chemical complexes;parts for timepieces, metallic tableware, jewels, ornaments such asframes for glasses, and all other sorts of structural parts.

Examples

Next, Examples of the invention will be described.

1. Production of Sintered Body (Zr—Nb Based) Sample No. 1

(1) First, a metal powder having a composition shown in Table 1 producedby a water atomization method was prepared. This metal powder had anaverage particle diameter of 4.12 μm, a tap density of 4.15 g/cm³, and aspecific surface area of 0.21 m²/g.

The composition of the powder shown in Table 1 was identified anddetermined by an inductively coupled high-frequency plasma opticalemission spectrometry (ICP analysis method). In the ICP analysis, an ICPdevice (model: CIROS-120) manufactured by Rigaku Corporation was used.Further, in the identification and determination of C, a carbon-sulfuranalyzer (CS-200) manufactured by LECO Corporation was used. Further, inthe identification and determination of 0, an oxygen-nitrogen analyzer(TC-300/EF-300) manufactured by LECO Corporation was used.

(2) Subsequently, the metal powder and a mixture (organic binder) ofpolypropylene and a wax were weighed at a mass ratio of 9:1 and mixedwith each other, whereby a mixed starting material was obtained.

(3) Subsequently, this mixed starting material was kneaded using akneader, whereby a compound was obtained.

(4) Subsequently, this compound was molded using an injection moldingdevice under the following molding conditions, whereby a molded body wasproduced.

Molding Conditions

-   -   Material temperature: 150° C.    -   Injection pressure: 11 MPa (110 kgf/cm²)

(5) Subsequently, the obtained molded body was subjected to a heattreatment (degreasing treatment) under the following degreasingconditions, whereby a degreased body was obtained.

Degreasing Conditions

-   -   Degreasing temperature: 500° C.    -   Degreasing time: 1 hour (retention time at the degreasing        temperature)    -   Degreasing atmosphere: nitrogen atmosphere

(6) Subsequently, the obtained degreased body was fired under thefollowing firing conditions, whereby a sintered body was obtained. Theshape of the sintered body was determined to be a cylinder with adiameter of 10 mm and a thickness of 5 mm.

Firing Conditions

-   -   Firing temperature: 1200° C.    -   Firing time: 3 hours (retention time at the firing temperature)    -   Firing atmosphere: argon atmosphere

Sample Nos. 2 to 30

Sintered bodies were obtained in the same manner as the method forproducing the sintered body of sample No. 1 except that the compositionand the like of the metal powder for powder metallurgy were changed asshown in Table 1, respectively. The sintered body of sample No. 30 wasobtained by performing an HIP treatment under the following conditionsafter firing. Further, the sintered bodies of sample Nos. 18 to 20 wereobtained by using the metal powder produced by a gas atomization method,respectively, and indicated by “gas” in the column of Remarks in Table1.

HIP Treatment Conditions

-   -   Heating temperature: 1100° C.    -   Heating time: 2 hours    -   Applied pressure: 100 MPa

TABLE 1 Metal powder for powder metallurgy Alloy composition E1 E2 E1 +(E1 + (E1 + Sample Cr Ni Si C (Zr) (Nb) Mo Mn O Fe E1/E2 E2 E2)/Si E2)/CRemarks No. — mass % — mass % — — — No. 1 Example 16.43 12.48 0.73 0.0180.09 0.07 2.11 0.06 0.28 remainder 1.29 0.16 0.22 8.89 No. 2 Example17.12 12.63 0.58 0.023 0.07 0.05 2.43 0.12 0.31 remainder 1.40 0.12 0.215.22 No. 3 Example 17.87 13.24 0.65 0.029 0.05 0.09 2.04 0.07 0.42remainder 0.56 0.14 0.22 4.83 No. 4 Example 16.19 14.71 0.84 0.011 0.050.05 2.89 0.08 0.25 remainder 1.00 0.10 0.12 9.09 No. 5 Example 17.5513.88 0.75 0.026 0.09 0.10 2.61 0.11 0.36 remainder 0.90 0.19 0.25 7.31No. 6 Example 16.79 11.58 0.52 0.068 0.12 0.03 2.74 0.12 0.22 remainder4.00 0.15 0.29 2.21 No. 7 Example 17.49 13.21 0.69 0.054 0.03 0.12 2.150.79 0.41 remainder 0.25 0.15 0.22 2.78 No. 8 Example 16.88 14.15 0.770.024 0.24 0.09 2.23 0.28 0.48 remainder 2.67 0.33 0.43 13.75 No. 9Example 17.32 12.65 0.48 0.021 0.08 0.26 2.81 0.17 0.29 remainder 0.310.34 0.71 16.19 No. 10 Example 17.25 12.87 0.35 0.065 0.09 0.05 2.150.35 0.62 remainder 1.80 0.14 0.40 2.15 No. 11 Example 17.66 12.55 0.960.017 0.07 0.07 2.24 0.05 0.25 remainder 1.00 0.14 0.15 8.24 No. 12Example 16.87 12.91 1.12 0.025 0.15 0.19 2.13 0.05 0.25 remainder 0.790.34 0.30 13.60 No. 13 Example 16.78 12.19 0.54 0.019 0.36 0.42 2.250.07 0.58 remainder 0.86 0.78 1.44 41.05 No. 14 Example 16.77 12.89 0.910.024 0.14 0.17 2.13 0.05 0.25 remainder 0.82 0.31 0.34 12.92 No. 15Example 16.47 12.57 0.87 0.023 0.13 0.15 2.04 0.05 0.25 remainder 0.870.28 0.32 12.17 No. 16 Example 16.75 12.58 0.68 0.007 0.05 0.09 2.840.12 0.28 remainder 0.56 0.14 0.21 20.00 No. 17 Example 17.22 13.54 0.840.152 0.08 0.05 2.84 0.12 0.28 remainder 1.60 0.13 0.15 0.86 No. 18Example 16.45 12.55 0.72 0.023 0.08 0.08 1.95 0.08 0.07 remainder 1.000.16 0.22 6.96 gas No. 19 Example 17.26 12.57 0.59 0.032 0.07 0.06 2.640.02 0.08 remainder 1.17 0.13 0.22 4.06 gas No. 20 Example 17.64 13.410.63 0.015 0.04 0.07 2.04 0.06 0.10 remainder 0.57 0.11 0.17 7.33 gasNo. 21 Comparative 16.34 12.84 0.75 0.025 0.00 0.07 2.36 0.11 0.29remainder 0.00 0.07 0.09 2.80 Example No. 22 Comparative 17.22 13.320.79 0.032 0.05 0.00 2.28 0.09 0.31 remainder — 0.05 0.06 1.56 ExampleNo. 23 Comparative 16.75 14.23 0.75 0.015 0.00 0.00 2.33 0.12 0.33remainder — 0.00 0.00 0.00 Example No. 24 Comparative 16.43 12.45 0.880.021 0.68 0.07 2.58 0.11 0.38 remainder 9.71 0.75 0.85 35.71 ExampleNo. 25 Comparative 16.35 13.04 0.66 0.035 0.06 0.71 2.36 0.05 0.41remainder 0.08 0.77 1.17 22.00 Example No. 26 Comparative 17.56 13.250.15 0.011 0.06 0.07 2.77 0.11 0.27 remainder 0.86 0.13 0.87 11.82Example No. 27 Comparative 17.63 13.54 0.95 0.061 0.04 0.08 2.89 0.320.45 remainder 0.50 0.12 0.06 1.97 Example No. 28 Comparative 17.5613.25 0.66 0.002 0.01 0.01 2.77 0.11 0.27 remainder 1.00 0.02 0.03 10.00Example No. 29 Comparative 17.56 13.25 0.35 0.380 0.22 0.07 2.68 0.240.45 remainder 3.14 0.29 0.83 0.76 Example No. 30 Comparative 16.3412.84 0.75 0.025 0.00 0.07 2.36 0.11 0.29 remainder — 0.07 0.09 2.80 HIPExample treatment

In Table 1, among the sintered bodies of the respective sample Nos.,those corresponding to the invention are indicated by “Example”, andthose not corresponding to the invention are indicated by “ComparativeExample”.

Each sintered body contained very small amounts of impurities, but thedescription thereof in Table 1 is omitted.

Sample Nos. 31 to 48

Sintered bodies were obtained in the same manner as the method forproducing the sintered body of sample No. 1 except that the compositionand the like of the metal powder for powder metallurgy were changed asshown in Table 2, respectively. The sintered body of sample No. 48 wasobtained by performing an HIP treatment under the following conditionsafter firing. Further, the sintered bodies of sample Nos. 41 to 43 wereobtained by using the metal powder produced by a gas atomization method,respectively, and indicated by “gas” in the column of Remarks in Table2.

HIP Treatment Conditions

-   -   Heating temperature: 1100° C.        -   Heating time: 2 hours    -   Applied pressure: 100 MPa

TABLE 2 Metal powder for powder metallurgy Alloy composition E1 E2 E1 +(E1 + (E1 + Sample Cr Ni Si C (Zr) (Nb) Mo Mn O Fe E1/E2 E2 E2)/Si E2)/CRemarks No. — mass % — mass % — — — No. 31 Example 18.94 13.59 0.770.048 0.11 0.09 3.48 0.08 0.48 remainder 1.22 0.20 0.26 4.17 No. 32Example 18.15 14.75 0.51 0.021 0.08 0.08 3.08 0.95 0.42 remainder 1.000.16 0.31 7.62 No. 33 Example 19.63 11.39 0.32 0.074 0.09 0.05 3.92 0.350.62 remainder 1.80 0.14 0.44 1.89 No. 34 Example 18.67 13.44 0.98 0.0650.18 0.04 3.32 0.07 0.28 remainder 4.50 0.22 0.22 3.38 No. 35 Example18.03 14.87 0.51 0.005 0.04 0.08 3.15 0.02 0.35 remainder 0.50 0.12 0.2424.00 No. 36 Example 19.78 12.35 0.42 0.178 0.09 0.08 3.87 0.35 0.62remainder 1.13 0.17 0.40 0.96 No. 37 Example 18.65 13.42 0.87 0.061 0.170.04 3.29 0.07 0.28 remainder 4.25 0.21 0.24 3.44 No. 38 Example 18.6313.46 0.94 0.063 0.16 0.05 3.27 0.07 0.28 remainder 3.20 0.21 0.22 3.33No. 39 Example 22.54 13.59 0.86 0.066 0.08 0.08 0.00 0.09 0.26 remainder1.00 0.16 0.19 2.42 No. 40 Example 25.41 21.36 1.16 0.053 0.06 0.08 0.000.07 0.27 remainder 0.75 0.14 0.12 2.64 No. 41 Example 18.88 13.54 0.870.056 0.12 0.11 3.52 0.11 0.12 remainder 1.09 0.23 0.26 4.11 gas No. 42Example 18.21 14.81 0.48 0.025 0.07 0.09 3.11 0.98 0.11 remainder 0.780.16 0.33 6.40 gas No. 43 Example 19.57 11.44 0.31 0.068 0.08 0.06 4.020.51 0.16 remainder 1.33 0.14 0.45 2.06 gas No. 44 Comparative 18.8711.24 0.57 0.056 0.00 0.07 3.47 0.22 0.29 remainder 0.00 0.07 0.12 1.25Example No. 45 Comparative 19.56 14.15 0.79 0.032 0.15 0.00 3.75 0.090.31 remainder — 0.15 0.19 4.69 Example No. 46 Comparative 18.78 11.420.88 0.012 0.58 0.07 2.58 0.11 0.38 remainder 8.29 0.65 0.74 54.17Example No. 47 Comparative 19.65 14.51 0.66 0.053 0.06 0.89 2.36 0.050.41 remainder 0.07 0.95 1.44 17.92 Example No. 48 Comparative 18.8711.24 0.57 0.056 0.00 0.07 3.47 0.22 0.29 remainder 0.00 0.07 0.12 1.25HIP Example treatment

In Table 2, among the sintered bodies of the respective sample Nos.,those corresponding to the invention are indicated by “Example”, andthose not corresponding to the invention are indicated by “ComparativeExample”.

Each sintered body contained very small amounts of impurities, but thedescription thereof in Table 2 is omitted.

Sample Nos. 49 to 66

Sintered bodies were obtained in the same manner as the method forproducing the sintered body of sample No. 1 except that the compositionand the like of the metal powder for powder metallurgy were changed asshown in Table 3, respectively. The sintered body of sample No. 66 wasobtained by performing an HIP treatment under the following conditionsafter firing. Further, the sintered bodies of sample Nos. 59 to 61 wereobtained by using the metal powder produced by a gas atomization method,respectively, and indicated by “gas” in the column of Remarks in Table3.

HIP Treatment Conditions

-   -   Heating temperature: 1100° C.    -   Heating time: 2 hours    -   Applied pressure: 100 MPa

TABLE 3 Metal powder for powder metallurgy Alloy composition E1 E2 E1 +(E1 + (E1 + Sample Cr Ni Si C (Zr) (Nb) Mo Mn O Fe E1/E2 E2 E2)/Si E2)/CRemarks No. — mass % — mass % — — — No. 49 Example 19.21 8.34 0.62 0.0380.08 0.06 0.00 0.21 0.48 remainder 1.33 0.14 0.23 3.68 No. 50 Example19.74 9.56 0.88 0.041 0.05 0.10 0.08 0.04 0.55 remainder 0.50 0.15 0.173.66 No. 51 Example 18.30 10.12 0.44 0.019 0.15 0.09 0.05 0.07 0.68remainder 1.67 0.24 0.55 12.63 No. 52 Example 19.35 8.19 1.05 0.069 0.080.06 0.00 0.05 0.18 remainder 1.33 0.14 0.13 2.03 No. 53 Example 19.459.65 0.88 0.007 0.05 0.10 0.08 0.00 0.55 remainder 0.50 0.15 0.17 21.43No. 54 Example 18.25 10.25 0.44 0.256 0.15 0.09 0.05 0.07 0.68 remainder1.67 0.24 0.55 0.94 No. 55 Example 20.58 21.54 1.15 0.074 0.05 0.09 0.001.23 0.75 remainder 0.56 0.14 0.12 1.89 No. 56 Example 20.34 19.25 1.020.068 0.05 0.09 0.00 1.23 0.75 remainder 0.56 0.14 0.14 2.06 No. 57Example 16.58 7.45 0.56 0.128 0.06 0.08 0.05 0.48 0.25 remainder 0.750.14 0.25 1.09 No. 58 Example 15.72 10.25 0.36 0.058 0.04 0.09 2.54 0.070.21 remainder 0.44 0.13 0.36 2.24 No. 59 Example 19.11 8.43 0.64 0.0450.07 0.07 0.00 0.23 0.12 remainder 1.00 0.14 0.22 3.11 gas No. 60Example 19.72 9.65 0.85 0.048 0.06 0.11 0.09 0.05 0.14 remainder 0.550.17 0.20 3.54 gas No. 61 Example 18.25 10.21 0.46 0.015 0.12 0.12 0.060.09 0.18 remainder 1.00 0.24 0.52 16.00 gas No. 62 Comparative 19.118.48 0.74 0.064 0.00 0.05 0.00 0.18 0.28 remainder 0.00 0.05 0.07 0.78Example No. 63 Comparative 18.78 9.77 0.79 0.023 0.08 0.00 0.02 0.090.31 remainder — 0.08 0.10 3.48 Example No. 64 Comparative 18.42 8.210.39 0.012 0.69 0.07 0.03 0.11 0.38 remainder 9.86 0.76 1.95 62.33Example No. 65 Comparative 19.21 8.55 0.42 0.021 0.06 0.61 0.02 0.150.32 remainder 0.10 0.67 1.60 31.90 Example No. 66 Comparative 19.118.48 0.74 0.064 0.00 0.05 0.00 0.18 0.28 remainder 0.00 0.05 0.07 0.78HIP Example treatment

In Table 3, among the sintered bodies of the respective sample Nos.,those corresponding to the invention are indicated by “Example”, andthose not corresponding to the invention are indicated by “ComparativeExample”.

Each sintered body contained very small amounts of impurities, but thedescription thereof in Table 3 is omitted.

Sample No. 67

(1) First, a metal powder having a composition shown in Table 4 wasproduced by a water atomization method in the same manner as in the caseof sample No. 1.

(2) Subsequently, the metal powder was granulated by a spray dryingmethod. The binder used at this time was polyvinyl alcohol, which wasused in an amount of 1 part by mass with respect to 100 parts by mass ofthe metal powder. Further, a solvent (ion exchanged water) was used inan amount of 50 parts by mass with respect to 1 part by mass ofpolyvinyl alcohol. In this manner, a granulated powder having an averageparticle diameter of 50 μm was obtained.

(3) Subsequently, this granulated powder was compact-molded under thefollowing molding conditions. In this molding, a press molding machinewas used. The shape of the molded body to be produced was determined tobe a cube with a side length of 20 mm.

Molding Conditions

-   -   Material temperature: 90° C.    -   Molding pressure: 600 MPa (6 t/cm²)

(4) Subsequently, the obtained molded body was subjected to a heattreatment (degreasing treatment) under the following degreasingconditions, whereby a degreased body was obtained.

Degreasing Conditions

-   -   Degreasing temperature: 450° C.    -   Degreasing time: 2 hours (retention time at the degreasing        temperature)    -   Degreasing atmosphere: nitrogen atmosphere

(5) Subsequently, the obtained degreased body was fired under thefollowing firing conditions, whereby a sintered body was obtained.

Firing Conditions

-   -   Firing temperature: 1200° C.    -   Firing time: 3 hours (retention time at the firing temperature)    -   Firing atmosphere: argon atmosphere

Sample Nos. 68 to 85

Sintered bodies were obtained in the same manner as in the case ofsample No. 67 except that the composition and the like of the metalpowder for powder metallurgy were changed as shown in Table 4,respectively. The sintered body of sample No. 85 was obtained byperforming an HIP treatment under the following conditions after firing.

HIP Treatment Conditions

-   -   Heating temperature: 1100° C.    -   Heating time: 2 hours    -   Applied pressure: 100 MPa

TABLE 4 Metal powder for powder metallurgy Alloy composition E1 E2 E1 +(E1 + (E1 + Sample Cr Ni Si C (Zr) (Nb) Mo Mn O Fe E1/E2 E2 E2)/Si E2)/CRemarks No. — mass % — mass % — — — No. 67 Example 16.43 12.48 0.730.018 0.09 0.07 2.11 0.06 0.28 remainder 1.29 0.16 0.22 8.89 Powdercompacting No. 68 Example 17.12 12.63 0.58 0.023 0.07 0.05 2.43 0.120.31 remainder 1.40 0.12 0.21 5.22 Powder compacting No. 69 Example17.87 13.24 0.65 0.029 0.05 0.09 2.04 0.07 0.42 remainder 0.56 0.14 0.224.83 Powder compacting No. 70 Example 16.19 14.71 0.84 0.011 0.05 0.052.89 0.08 0.25 remainder 1.00 0.10 0.12 9.09 Powder compacting No. 71Example 17.55 13.88 0.75 0.026 0.09 0.10 2.61 0.11 0.36 remainder 0.900.19 0.25 7.31 Powder compacting No. 72 Example 16.79 11.58 0.52 0.0680.12 0.03 2.74 0.12 0.22 remainder 4.00 0.15 0.29 2.21 Powder compactingNo. 73 Example 17.49 13.21 0.69 0.054 0.03 0.12 2.15 0.79 0.41 remainder0.25 0.15 0.22 2.78 Powder compacting No. 74 Example 16.88 14.15 0.770.024 0.24 0.09 2.23 0.28 0.48 remainder 2.67 0.33 0.43 13.75 Powdercompacting No. 75 Example 17.32 12.65 0.48 0.021 0.08 0.26 2.81 0.170.29 remainder 0.31 0.34 0.71 16.19 Powder compacting No. 76 Example17.25 12.87 0.35 0.065 0.09 0.05 2.15 0.35 0.62 remainder 1.80 0.14 0.402.15 Powder compacting No. 77 Example 17.66 12.55 0.96 0.017 0.07 0.072.24 0.05 0.25 remainder 1.00 0.14 0.15 8.24 Powder compacting No. 78Example 16.87 12.91 1.12 0.025 0.15 0.19 2.13 0.05 0.25 remainder 0.790.34 0.30 13.60 Powder compacting No. 79 Example 16.78 12.19 0.54 0.0190.36 0.42 2.25 0.07 0.58 remainder 0.86 0.78 1.44 41.05 Powdercompacting No. 80 Comparative 16.34 12.84 0.75 0.025 0.00 0.07 2.36 0.110.29 remainder 0.00 0.07 0.09 2.80 Powder Example compacting No. 81Comparative 17.22 13.32 0.79 0.032 0.05 0.00 2.28 0.09 0.31 remainder —0.05 0.06 1.56 Powder Example compacting No. 82 Comparative 16.75 14.230.75 0.015 0.00 0.00 2.33 0.12 0.33 remainder — 0.00 0.00 0.00 PowderExample compacting No. 83 Comparative 16.43 12.45 0.88 0.021 0.68 0.072.58 0.11 0.38 remainder 9.71 0.75 0.85 35.71 Powder Example compactingNo. 84 Comparative 16.35 13.04 0.66 0.035 0.06 0.71 2.36 0.05 0.41remainder 0.08 0.77 1.17 22.00 Powder Example compacting No. 85Comparative 16.34 12.84 0.75 0.025 0.00 0.07 2.36 0.11 0.29 remainder —0.07 0.09 2.80 HIP Example treatment

In Table 4, among the metal powders for powder metallurgy and thesintered bodies of the respective sample Nos., those corresponding tothe invention are indicated by “Example”, and those not corresponding tothe invention are indicated by “Comparative Example”.

Each sintered body contained very small amounts of impurities, but thedescription thereof in Table 4 is omitted.

2. Evaluation of Sintered Body (Zr—Nb Based) 2.1 Evaluation of RelativeDensity

With respect to the sintered bodies of the respective sample Nos. shownin Tables 1 to 4, the sintered density was measured in accordance withthe method for measuring the density of sintered metal materialsspecified in JIS Z 2501 (2000), and also the relative density of eachsintered body was calculated with reference to the true density of themetal powder for powder metallurgy used for producing each sinteredbody.

The calculation results are shown in Tables 5 to 8.

2.2 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shownin Tables 1 to 4, the Vickers hardness was measured in accordance withthe Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Tables 5 to 8.

2.3 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shownin Tables 1 to 4, the tensile strength, 0.2% proof stress, andelongation were measured in accordance with the metal material tensiletest method specified in JIS Z 2241 (2011).

Then, the measured values of these physical properties were evaluatedaccording to the following evaluation criteria.

Evaluation Criteria for Tensile Strength (Tables 5 and 8)

A: The tensile strength of the sintered body is 520 MPa or more.

B: The tensile strength of the sintered body is 510 MPa or more and lessthan 520 MPa.

C: The tensile strength of the sintered body is 500 MPa or more and lessthan 510 MPa.

D: The tensile strength of the sintered body is 490 MPa or more and lessthan 500 MPa.

E: The tensile strength of the sintered body is 480 MPa or more and lessthan 490 MPa.

F: The tensile strength of the sintered body is less than 480 MPa.

Evaluation Criteria for Tensile Strength (Tables 6 and 7)

A: The tensile strength of the sintered body is 560 MPa or more.

B: The tensile strength of the sintered body is 550 MPa or more and lessthan 560 MPa.

C: The tensile strength of the sintered body is 540 MPa or more and lessthan 550 MPa.

D: The tensile strength of the sintered body is 530 MPa or more and lessthan 540 MPa.

E: The tensile strength of the sintered body is 520 MPa or more and lessthan 530 MPa.

F: The tensile strength of the sintered body is less than 520 MPa.

Evaluation Criteria for 0.2% Proof Stress (Tables 5 and 8)

A: The 0.2% proof stress of the sintered body is 195 MPa or more.

B: The 0.2% proof stress of the sintered body is 190 MPa or more andless than 195 MPa.

C: The 0.2% proof stress of the sintered body is 185 MPa or more andless than 190 MPa.

D: The 0.2% proof stress of the sintered body is 180 MPa or more andless than 185 MPa.

E: The 0.2% proof stress of the sintered body is 175 MPa or more andless than 180 MPa.

F: The 0.2% proof stress of the sintered body is less than 175 MPa.

Evaluation Criteria for 0.2% Proof Stress (Tables 6 and 7)

A: The 0.2% proof stress of the sintered body is 225 MPa or more.

B: The 0.2% proof stress of the sintered body is 220 MPa or more andless than 225 MPa.

C: The 0.2% proof stress of the sintered body is 215 MPa or more andless than 220 MPa.

D: The 0.2% proof stress of the sintered body is 210 MPa or more andless than 215 MPa.

E: The 0.2% proof stress of the sintered body is 205 MPa or more andless than 210 MPa.

F: The 0.2% proof stress of the sintered body is less than 205 MPa.

Evaluation Criteria for Elongation

A: The elongation of the sintered body is 48% or more.

B: The elongation of the sintered body is 46% or more and less than 48%.

C: The elongation of the sintered body is 44% or more and less than 46%.

D: The elongation of the sintered body is 42% or more and less than 44%.

E: The elongation of the sintered body is 40% or more and less than 42%.

F: The elongation of the sintered body is less than 40%.

The above evaluation results are shown in Tables 5 to 8. As describedabove, the evaluation criteria are different between Tables 5 and 8 andTables 6 and 7.

2.4 Evaluation of Fatigue Strength

With respect to the sintered bodies of the respective sample Nos. shownin Tables 1 to 4, the fatigue strength was measured.

The fatigue strength was measured in accordance with the test methodspecified in JIS Z 2273 (1978). The waveform of an applied loadcorresponding to a repeated stress was set to an alternating sine wave,and the minimum/maximum stress ratio (minimum stress/maximum stress) wasset to 0.1. Further, the repeated frequency was set to 30 Hz, and therepeat count was set to 1×10⁷.

Then, the measured fatigue strength was evaluated according to thefollowing evaluation criteria.

Evaluation Criteria for Fatigue Strength

A: The fatigue strength of the sintered body is 260 MPa or more.

B: The fatigue strength of the sintered body is 240 MPa or more and lessthan 260 MPa.

C: The fatigue strength of the sintered body is 220 MPa or more and lessthan 240 MPa.

D: The fatigue strength of the sintered body is 200 MPa or more and lessthan 220 MPa.

E: The fatigue strength of the sintered body is 180 MPa or more and lessthan 200 MPa.

F: The fatigue strength of the sintered body is less than 180 MPa.

The above evaluation results are shown in Tables 5 to 8.

TABLE 5 Metal powder Evaluation results of sintered body Average par-Relative Vickers Tensile 0.2% proof Fatigue Sample ticle diameterdensity hardness strength stress Elongation strength No. — μm % — — — —— No. 1 Example 4.05 99.5 165 A A A A No. 2 Example 3.79 99.6 175 A A AA No. 3 Example 3.84 99.3 171 A A A A No. 4 Example 3.92 98.8 153 B A AA No. 5 Example 4.56 99.7 182 A A A A No. 6 Example 3.68 98.7 154 B B AB No. 7 Example 3.77 98.8 156 B B A B No. 8 Example 3.81 98.3 149 B B AB No. 9 Example 3.85 98.1 148 B B B B No. 10 Example 4.23 98.5 152 B B AB No. 11 Example 3.21 98.1 146 B B B B No. 12 Example 3.36 97.8 144 B BC B No. 13 Example 6.18 97.6 142 C C C C No. 14 Example 10.8 97.5 144 BC C C No. 15 Example 15.4 97.2 141 C C C C No. 16 Example 5.23 97.8 141B B B B No. 17 Example 4.42 97.3 163 B B C B No. 18 Example 8.11 99.3161 A A A A No. 19 Example 7.65 99.4 171 A A A A No. 20 Example 7.2599.1 164 A A A A No. 21 Comparative 3.77 96.4 128 D D B D Example No. 22Comparative 3.94 96.8 134 D D B D Example No. 23 Comparative 3.65 96.2123 E E C E Example No. 24 Comparative 4.87 94.7 115 D D D D Example No.25 Comparative 4.25 94.6 118 D D E D Example No. 26 Comparative 3.6494.5 102 E E C E Example No. 27 Comparative 3.55 92.6 135 F F E FExample No. 28 Comparative 4.87 95.3 118 D D B D Example No. 29Comparative 4.66 93.2 138 E E F E Example No. 30 Comparative 3.77 99.2175 A A B A Example

TABLE 6 Metal powder Evaluation results of sintered body Average par-Relative Vickers Tensile 0.2% proof Fatigue Sample ticle diameterdensity hardness strength stress Elongation strength No. — μm % — — — —— No. 31 Example 5.68 99.3 178 A A A A No. 32 Example 4.79 99.5 185 A AA A No. 33 Example 4.05 98.6 167 B B A B No. 34 Example 3.81 98.8 158 BB A B No. 35 Example 3.05 98.2 162 B B B B No. 36 Example 4.25 97.6 154B B C B No. 37 Example 9.86 97.8 158 B B B B No. 38 Example 14.2 97.5154 B C C C No. 39 Example 2.56 98.6 171 B B A A No. 40 Example 14.298.3 173 B B A A No. 41 Example 11.53 99.1 174 A A A A No. 42 Example9.64 99.2 180 A A A A No. 43 Example 8.25 98.3 163 B B A B No. 44Comparative 5.32 96.4 127 D D B D Example No. 45 Comparative 5.48 96.7136 D D B D Example No. 46 Comparative 4.23 95.2 121 D D D D Example No.47 Comparative 4.51 94.8 105 E E F E Example No. 48 Comparative 5.3299.2 174 A A B A Example

TABLE 7 Metal powder Evaluation results of sintered body Average par-Relative Vickers Tensile 0.2% proof Fatigue Sample ticle diameterdensity hardness strength stress Elongation strength No. — μm % — — — —— No. 49 Example 3.97 99.6 172 A A A A No. 50 Example 3.25 99.3 167 A AB A No. 51 Example 6.54 98.4 142 A A B A No. 52 Example 5.48 98.2 157 BB B B No. 53 Example 3.92 98.4 161 B B B B No. 54 Example 3.74 97.3 148B B C B No. 55 Example 16.45 97.1 137 C C C C No. 56 Example 22.1 97.0135 C C C C No. 57 Example 10.05 97.5 138 B B B B No. 58 Example 7.2398.8 165 B B A B No. 59 Example 8.12 99.3 165 A A A A No. 60 Example7.22 99.0 160 A A B A No. 61 Example 13.65 98.2 134 A A B A No. 62Comparative 3.89 96.3 127 D D B D Example No. 63 Comparative 3.47 96.7136 D D B D Example No. 64 Comparative 4.25 94.7 116 D D D D Example No.65 Comparative 3.64 95.2 119 D D E D Example No. 66 Comparative 3.8999.4 170 A A B A Example

TABLE 8 Metal powder Evaluation results of sintered body Average par-Relative Vickers Tensile 0.2% proof Fatigue Sample ticle diameterdensity hardness strength stress Elongation strength No. — μm % — — — —— No. 67 Example 4.05 99.6 168 A A A A No. 68 Example 3.79 99.6 177 A AA A No. 69 Example 3.84 99.4 172 A A A A No. 70 Example 3.92 98.9 155 BA A A No. 71 Example 4.56 99.7 183 A A A A No. 72 Example 3.68 98.9 158B B A B No. 73 Example 3.77 99.0 162 B B A B No. 74 Example 3.81 98.5155 B B A B No. 75 Example 3.85 98.4 156 B B B B No. 76 Example 4.2398.7 157 B B A B No. 77 Example 3.21 98.4 159 B B B B No. 78 Example3.36 98.1 150 B B C B No. 79 Example 6.18 97.9 146 C C C C No. 80Comparative 3.77 96.6 129 D D B D Example No. 81 Comparative 3.94 96.9136 D D B D Example No. 82 Comparative 3.65 96.4 128 E E C E Example No.83 Comparative 4.87 94.9 119 D D D D Example No. 84 Comparative 4.2594.8 125 D D E D Example No. 85 Comparative 3.77 99.3 180 A A B AExample

As apparent from Tables 5 to 8, it was confirmed that the sinteredbodies corresponding to Example each have a higher relative density thanthe sintered bodies corresponding to Comparative Example (excluding thesintered bodies having undergone the HIP treatment). Further, it wasalso confirmed that there is a significant difference in properties suchas tensile strength, 0.2% proof stress, elongation, and fatigue strengthbetween the sintered bodies corresponding to Example and the sinteredbodies corresponding to Comparative Example (excluding the sinteredbodies having undergone the HIP treatment).

On the other hand, by comparison of the values of the respectivephysical properties between the sintered bodies corresponding to Exampleand the sintered bodies having undergone the HIP treatment, it wasconfirmed that the values of the physical properties are all comparableto each other.

2.5 Observation of Cross Section of Sintered Body Using ScanningElectron Microscope (SEM)

An observation image was obtained for the cross section of each sinteredbody corresponding to Example using a scanning electron microscope(JXA-8500F, manufactured by JEOL Ltd.). When the image was taken, theacceleration voltage was set to 15 kV, and the magnification was set to10000.

As a result of observation, a region in the form of a particle (firstregion) which appears dark in color and a region (second region) whichis located surrounding the first region and appears light in color wereobserved in the observation image of the cross section of each sinteredbody. Therefore, when the average of the circle equivalent diameter ofthe first region was determined, it was about 2 μm or more and 8 μm orless in all the sintered bodies.

Subsequently, a qualitative and quantitative analysis of the observationregion was performed using an electron beam microanalyzer. As a result,in the first region, the sum of the content of Si and the content of Owas 2.5 times to 3.5 times the content of Fe. Further, the content of Siin the first region was 14 times or more the content of Si in the secondregion. Further, the content of Zr in the first region was 3 times ormore the content of Zr in the second region.

Based on the above results, it was confirmed that in the sintered bodiescorresponding to Example, silicon oxide is accumulated by using a Zrcarbide or the like as a nucleus.

The above results revealed that according to the invention, a highdensity and excellent mechanical properties can be provided to thesintered body in the same manner as in the case of performing an HIPtreatment even if an additional treatment of increasing the density suchas an HIP treatment is not performed.

In addition, when a crystal structure analysis was performed for thesintered bodies corresponding to Example by X-ray diffractometry, it wasconfirmed that all the sintered bodies mainly have an austenite crystalstructure.

3. Production of Sintered Body (Hf—Nb Based) Sample Nos. 86 to 113

Sintered bodies were obtained in the same manner as the method forproducing the sintered body of sample No. 1 except that the compositionand the like of the metal powder for powder metallurgy were changed asshown in Tables 9 to 11, respectively.

TABLE 9 Metal powder for powder metallurgy Alloy composition E1 E2 E1 +(E1 + (E1 + Sample Cr Ni Si C (Hf) (Nb) Mo Mn O Fe E1/E2 E2 E2)/Si E2)/CRemarks No. — mass % — mass % — — — No. 86 Example 16.25 12.56 0.71 0.020.09 0.05 2.09 0.05 0.25 remainder 1.80 0.14 0.20 8.24 No. 87 Example17.14 12.54 0.57 0.02 0.07 0.05 2.45 0.09 0.32 remainder 1.40 0.12 0.215.45 No. 88 Example 17.78 13.25 0.53 0.03 0.07 0.08 2.06 0.08 0.41remainder 0.88 0.15 0.28 5.56 No. 89 Example 16.25 14.68 0.82 0.01 0.060.03 2.89 0.08 0.25 remainder 2.00 0.09 0.11 7.50 No. 90 Example 17.5213.87 0.74 0.03 0.09 0.10 2.63 0.11 0.34 remainder 0.90 0.19 0.26 7.31No. 91 Example 16.82 12.03 0.53 0.07 0.11 0.04 2.76 0.11 0.23 remainder2.75 0.15 0.28 2.17 No. 92 Example 17.52 13.25 0.68 0.06 0.07 0.12 2.210.78 0.41 remainder 0.58 0.19 0.28 3.45 No. 93 Comparative 16.34 12.840.75 0.03 0.00 0.07 2.36 0.11 0.29 remainder 0.00 0.07 0.09 2.80 ExampleNo. 94 Comparative 17.25 13.35 0.82 0.03 0.08 0.00 2.23 0.09 0.32remainder — 0.08 0.10 2.86 Example No. 95 Comparative 16.75 14.23 0.750.02 0.00 0.00 2.33 0.12 0.33 remainder — 0.00 0.00 0.00 Example No. 96Comparative 16.34 12.54 0.87 0.02 0.71 0.05 2.56 0.11 0.36 remainder14.20  0.76 0.87 36.19 Example No. 97 Comparative 16.44 13.12 1.65 0.030.04 0.68 2.41 0.06 0.42 remainder 0.06 0.72 1.11 21.18 Example No. 98Comparative 17.63 13.21 0.14 0.01 0.06 0.07 2.77 0.11 0.27 remainder0.86 0.13 0.93 10.83 Example No. 99 Comparative 17.54 13.33 0.91 0.050.07 0.05 2.68 0.34 0.48 remainder 1.40 0.12 0.06 2.22 Example

TABLE 10 Metal powder for powder metallurgy Alloy composition E1 E2 E1 +(E1 + (E1 + Sample Cr Ni Si C (Hf) (Nb) Mo Mn O Fe E1/E2 E2 E2)/Si E2)/CRemarks No. — mass % — mass % — — — No. 100 Example 18.96 13.54 0.820.041 0.09 0.05 3.55 0.35 0.41 remainder 1.80 0.14 0.17 3.14 No. 101Example 18.25 14.86 0.54 0.021 0.06 0.09 3.12 0.87 0.39 remainder 0.670.15 0.28 7.14 No. 102 Example 19.74 11.32 0.34 0.067 0.09 0.09 3.880.45 0.55 remainder 1.00 0.18 0.53 2.69 No. 103 Comparative 18.67 11.360.78 0.053 0.00 0.07 3.47 0.22 0.29 remainder 0.00 0.07 0.09 1.32Example No. 104 Comparative 19.54 14.35 0.89 0.022 0.11 0.00 3.75 0.090.31 remainder — 0.11 0.12 5.00 Example No. 105 Comparative 18.69 11.870.71 0.027 0.54 0.07 3.76 0.12 0.38 remainder 7.71 0.61 0.86 22.59Example No. 106 Comparative 19.42 14.58 0.62 0.024 0.06 0.66 3.54 0.070.41 remainder 0.09 0.72 1.16 30.00 Example

TABLE 11 Metal powder for powder metallurgy Alloy composition E1 E2 E1 +(E1 + (E1 + Sample Cr Ni Si C (Hf) (Nb) Mo Mn O Fe E1/E2 E2 E2)/Si E2)/CRemarks No. — mass % — mass % — — — No. 107 Example 19.21 8.25 0.670.035 0.08 0.05 0.00 0.18 0.25 remainder 1.60 0.13 0.19 3.71 No. 108Example 19.74 9.62 0.89 0.039 0.06 0.09 0.05 0.08 0.29 remainder 0.670.15 0.17 3.85 No. 109 Example 18.30 10.31 0.43 0.017 0.14 0.09 0.030.23 0.41 remainder 1.56 0.23 0.53 13.53 No. 110 Comparative 19.11 8.230.77 0.055 0.00 0.06 0.00 0.14 0.25 remainder 0.00 0.06 0.08 1.09Example No. 111 Comparative 18.78 9.45 0.76 0.024 0.07 0.00 0.02 0.110.29 remainder — 0.07 0.09 2.92 Example No. 112 Comparative 18.42 8.360.38 0.011 0.54 0.08 0.03 0.25 0.28 remainder 6.75 0.62 1.63 56.36Example No. 113 Comparative 19.21 8.45 0.45 0.018 0.06 0.58 0.04 0.160.32 remainder 1.10 0.64 1.42 35.56 Example

In Tables 9 to 11, among the sintered bodies of the respective sampleNos., those corresponding to the invention are indicated by “Example”,and those not corresponding to the invention are indicated by“Comparative Example”.

Each sintered body contained very small amounts of impurities, but thedescription thereof in Tables 9 to 11 is omitted.

4. Evaluation of Sintered Body (Hf—Nb Based) 4.1 Evaluation of RelativeDensity

With respect to the sintered bodies of the respective sample Nos. shownin Tables 9 to 11, the sintered density was measured in accordance withthe method for measuring the density of sintered metal materialsspecified in JIS Z 2501 (2000), and also the relative density of eachsintered body was calculated with reference to the true density of themetal powder for powder metallurgy used for producing each sinteredbody.

The calculation results are shown in Tables 12 to 14.

4.2 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shownin Tables 9 to 11, the Vickers hardness was measured in accordance withthe Vickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Tables 12 to 14.

4.3 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shownin Tables 9 to 11, the tensile strength, 0.2% proof stress, andelongation were measured in accordance with the metal material tensiletest method specified in JIS Z 2241 (2011).

Then, the values of the physical properties of the sintered bodies ofthe respective sample Nos. shown in Table 9 were evaluated according tothe above-mentioned evaluation criteria applied to the Tables 5 and 8,and the values of the physical properties of the sintered bodies of therespective sample Nos. shown in Tables 10 and 11 were evaluatedaccording to the above-mentioned evaluation criteria applied to theTables 6 and 7.

The evaluation results are shown in Tables 12 to 14.

TABLE 12 Metal powder Evaluation results of sintered body Average par-Relative Vickers Tensile 0.2% proof Sample ticle diameter densityhardness strength stress Elongation No. — μm % — — — — No. 86 Example4.12 99.5 162 A A A No. 87 Example 4.25 99.3 173 A A A No. 88 Example4.02 98.7 160 A A A No. 89 Example 3.88 98.5 153 B A A No. 90 Example4.56 98.9 175 A A A No. 91 Example 3.98 99.2 170 A A A No. 92 Example3.77 98.2 185 B B B No. 93 Comparative 3.86 96.4 185 D D B Example No.94 Comparative 3.95 96.8 180 D D B Example No. 95 Comparative 4.05 96.2192 E E C Example No. 96 Comparative 4.57 94.7 202 D D D Example No. 97Comparative 4.52 94.6 211 D D E Example No. 98 Comparative 3.65 94.6 195E E D Example No. 99 Comparative 3.28 93.4 214 F F E Example

TABLE 13 Metal powder Evaluation results of sintered body Average par-Relative Vickers Tensile 0.2% proof Sample ticle diameter densityhardness strength stress Elongation No. — μm % — — — — No. 100 Example5.86 99.1 167 A A A No. 101 Example 4.97 98.9 170 A A A No. 102 Example4.25 98.6 184 B B B No. 103 Comparative 5.31 96.3 195 D D B Example No.104 Comparative 5.83 96.6 189 D D B Example No. 105 Comparative 4.5295.1 201 D D D Example No. 106 Comparative 4.12 94.9 205 E E F Example

TABLE 14 Metal powder Evaluation results of sintered body Average par-Relative Vickers Tensile 0.2% proof Sample ticle diameter densityhardness strength stress Elongation No. — μm % — — — — No. 107 Example4.08 99.3 164 A A A No. 108 Example 3.58 99.0 175 A A A No. 109 Example6.41 98.5 182 A A B No. 110 Comparative 3.98 96.3 195 D D B Example No.111 Comparative 3.58 96.7 192 D D B Example No. 112 Comparative 4.3594.7 205 D D E Example No. 113 Comparative 4.56 95.2 201 D D E Example

As apparent from Tables 12 to 14, it was confirmed that the sinteredbodies corresponding to Example each have a higher relative density thanthe sintered bodies corresponding to Comparative Example. It was alsoconfirmed that there is a significant difference in properties such astensile strength, 0.2% proof stress, and elongation between the sinteredbodies corresponding to Example and the sintered bodies corresponding toComparative Example.

5. Production of Sintered Body (Ti—Nb Based) Sample Nos. 114 to 123

Sintered bodies were obtained in the same manner as the method forproducing the sintered body of sample No. 1 except that the compositionand the like of the metal powder for powder metallurgy were changed asshown in Table 15, respectively.

Sample No. 124

A metal powder having an average particle diameter of 4.62 μm, a Tipowder having an average particle diameter of 40 μm, and a Nb powderhaving an average particle diameter of 25 μm were mixed, whereby a mixedpowder was prepared. In the preparation of the mixed powder, each of themixing amounts of the metal powder, the Ti powder, and the Nb powder wasadjusted so that the composition of the mixed powder was as shown inTable 15.

Then, a sintered body was obtained in the same manner as the method forproducing the sintered body of sample No. 1 using this mixed powder.

TABLE 15 Metal powder for powder metallurgy Alloy composition E1 E2 E1 +(E1 + (E1 + Sample Cr Ni Si C (Ti) (Nb) Mo Mn O Fe E1/E2 E2 E2)/Si E2)/CRemarks No. — mass % — mass % — — — No. 114 Example 16.52 12.54 0.770.015 0.08 0.07 2.13 0.06 0.25 remainder 1.14 0.15 0.19 10.00 No. 115Example 16.86 13.15 0.51 0.021 0.08 0.08 2.21 0.51 0.42 remainder 1.000.16 0.31 7.62 No. 116 Example 16.63 11.87 0.81 0.025 0.06 0.10 2.070.35 0.24 remainder 0.60 0.16 0.20 6.40 No. 117 Example 17.12 12.61 0.980.065 0.04 0.18 2.23 0.07 0.54 remainder 0.22 0.22 0.22 3.38 No. 118Example 16.23 13.54 0.51 0.009 0.04 0.08 2.26 0.02 0.35 remainder 0.500.12 0.24 13.33 No. 119 Example 17.85 12.35 0.42 0.125 0.09 0.08 2.570.35 0.25 remainder 1.13 0.17 0.40 1.36 No. 120 Comparative 16.87 11.420.56 0.056 0.00 0.08 2.47 0.12 0.25 remainder 0.00 0.08 0.14 1.43Example No. 121 Comparative 17.56 14.51 0.78 0.032 0.12 0.00 2.68 0.110.33 remainder — 0.12 0.15 3.75 Example No. 122 Comparative 16.78 11.240.87 0.012 0.54 0.06 2.55 0.15 0.32 remainder 9.00 0.60 0.69 50.00Example No. 123 Comparative 17.65 14.15 0.68 0.053 0.08 0.89 2.63 0.060.25 remainder 0.09 0.97 1.43 18.30 Example No. 124 Comparative 16.8814.10 0.87 0.056 0.45 0.20 2.25 0.08 0.26 remainder 2.25 0.65 0.75 11.61Mixed Example powder

In Table 15, among the sintered bodies of the respective sample Nos.,those corresponding to the invention are indicated by “Example”, andthose not corresponding to the invention are indicated by “ComparativeExample”.

Each sintered body contained very small amounts of impurities, but thedescription thereof in Table 15 is omitted.

6. Evaluation of Sintered Body (Ti—Nb Based) 6.1 Evaluation of RelativeDensity

With respect to the sintered bodies of the respective sample Nos. shownin Table 15, the sintered density was measured in accordance with themethod for measuring the density of sintered metal materials specifiedin JIS Z 2501 (2000), and also the relative density of each sinteredbody was calculated with reference to the true density of the metalpowder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Table 16.

6.2 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shownin Table 15, the Vickers hardness was measured in accordance with theVickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 16.

6.3 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shownin Table 15, the tensile strength, 0.2% proof stress, and elongationwere measured in accordance with the metal material tensile test methodspecified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluatedaccording to the above-mentioned evaluation criteria applied to theTables 5 and 8.

The evaluation results are shown in Table 16.

TABLE 16 Metal powder Evaluation results of sintered body Average par-Relative Vickers Tensile 0.2% proof Sample ticle diameter densityhardness strength stress Elongation No. — μm % — — — — No. 114 Example4.34 98.9 179 A A A No. 115 Example 4.79 99.3 178 A A A No. 116 Example4.05 99.4 175 A A A No. 117 Example 3.89 98.7 180 B B A No. 118 Example4.12 98.5 185 B B B No. 119 Example 4.26 98.2 189 B B C No. 120Comparative 4.31 96.5 191 D D B Example No. 121 Comparative 4.48 96.6189 D D B Example No. 122 Comparative 4.25 95.3 205 D D D Example No.123 Comparative 4.36 94.7 215 E E F Example No. 124 Comparative 4.6295.9 214 E E F Example

As apparent from Table 16, it was confirmed that the sintered bodiescorresponding to Example each have a higher relative density than thesintered bodies corresponding to Comparative Example. It was alsoconfirmed that there is a significant difference in properties such astensile strength, 0.2% proof stress, and elongation between the sinteredbodies corresponding to Example and the sintered bodies corresponding toComparative Example.

7. Production of Sintered Body (Nb—Ta Based) Sample Nos. 125 to 134

Sintered bodies were obtained in the same manner as the method forproducing the sintered body of sample No. 1 except that the compositionand the like of the metal powder for powder metallurgy were changed asshown in Table 17, respectively.

TABLE 17 Metal powder for powder metallurgy Alloy composition E1 E2 E1 +(E1 + (E1 + Sample Cr Ni Si C (Nb) (Ta) Mo Mn O Fe E1/E2 E2 E2)/Si E2)/CRemarks No. — mass % — mass % — — — No. 125 Example 16.21 12.15 0.630.035 0.07 0.12 2.21 0.06 0.38 remainder 0.58 0.19 0.30 5.43 No. 126Example 16.74 11.36 0.87 0.042 0.05 0.10 2.26 0.05 0.45 remainder 0.500.15 0.17 3.57 No. 127 Example 16.30 10.25 0.45 0.018 0.12 0.09 2.680.07 0.58 remainder 1.33 0.21 0.47 11.67 No. 128 Example 16.35 13.681.03 0.067 0.05 0.08 2.77 0.06 0.22 remainder 0.63 0.13 0.13 1.94 No.129 Example 16.45 14.18 0.86 0.009 0.03 0.04 2.45 0.00 0.45 remainder0.75 0.07 0.08 7.78 No. 130 Example 16.25 12.35 0.47 0.123 0.15 0.092.12 0.08 0.48 remainder 1.67 0.24 0.51 1.95 No. 131 Comparative 17.1112.29 0.74 0.064 0.00 0.05 2.18 0.15 0.29 remainder 0.00 0.05 0.07 0.78Example No. 132 Comparative 16.78 12.48 0.79 0.023 0.08 0.00 2.06 0.120.33 remainder — 0.08 0.10 3.48 Example No. 133 Comparative 16.42 13.650.39 0.012 0.69 0.07 2.89 0.08 0.37 remainder 9.86 0.76 1.95 63.33Example No. 134 Comparative 17.21 10.88 0.42 0.021 0.06 0.61 2.98 0.130.35 remainder 0.10 0.67 1.60 31.90 Example

In Table 17, among the sintered bodies of the respective sample Nos.,those corresponding to the invention are indicated by “Example”, andthose not corresponding to the invention are indicated by “ComparativeExample”.

Each sintered body contained very small amounts of impurities, but thedescription thereof in Table 17 is omitted.

8. Evaluation of Sintered Body (Nb—Ta Based) 8.1 Evaluation of RelativeDensity

With respect to the sintered bodies of the respective sample Nos. shownin Table 17, the sintered density was measured in accordance with themethod for measuring the density of sintered metal materials specifiedin JIS Z 2501 (2000), and also the relative density of each sinteredbody was calculated with reference to the true density of the metalpowder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Table 18.

8.2 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shownin Table 17, the Vickers hardness was measured in accordance with theVickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 18. 8.3 Evaluation of TensileStrength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shownin Table 17, the tensile strength, 0.2% proof stress, and elongationwere measured in accordance with the metal material tensile test methodspecified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluatedaccording to the above-mentioned evaluation criteria applied to Tables 5and 8.

The evaluation results are shown in Table 18.

TABLE 18 Metal powder Evaluation results of sintered body Average par-Relative Vickers Tensile 0.2% proof Sample ticle diameter densityhardness strength stress Elongation No. — μm % — — — — No. 125 Example3.87 99.0 166 A A A No. 126 Example 4.12 99.1 167 A A B No. 127 Example6.45 98.5 173 A A B No. 128 Example 5.82 98.3 178 B B B No. 129 Example3.45 98.2 175 B B B No. 130 Example 3.25 97.4 181 B B C No. 131Comparative 3.98 96.3 187 D D B Example No. 132 Comparative 3.74 96.0198 D D B Example No. 133 Comparative 4.21 93.8 236 D D D Example No.134 Comparative 3.87 94.2 225 D D E Example

As apparent from Table 18, it was confirmed that the sintered bodiescorresponding to Example each have a higher relative density than thesintered bodies corresponding to Comparative Example. It was alsoconfirmed that there is a significant difference in properties such astensile strength, 0.2% proof stress, and elongation between the sinteredbodies corresponding to Example and the sintered bodies corresponding toComparative Example.

9. Production of Sintered Body (Y—Nb Based) Sample Nos. 135 to 145

Sintered bodies were obtained in the same manner as the method forproducing the sintered body of sample No. 1 except that the compositionand the like of the metal powder for powder metallurgy were changed asshown in Table 19, respectively.

TABLE 19 Metal powder for powder metallurgy Alloy composition E1 E2 E1 +(E1 + (E1 + Sample Cr Ni Si C (Y) (Nb) Mo Mn O Fe E1/E2 E2 E2)/Si E2)/CRemarks No. — mass % — mass % — — — No. 135 Example 16.55 12.58 0.850.025 0.08 0.09 2.13 0.07 0.26 remainder 0.89 0.17 0.20 6.80 No. 136Example 17.32 12.87 0.68 0.023 0.05 0.08 2.21 0.11 0.33 remainder 0.630.13 0.19 5.65 No. 137 Example 16.35 12.32 0.74 0.029 0.09 0.05 2.040.08 0.41 remainder 1.80 0.14 0.19 4.83 No. 138 Example 16.31 14.52 0.530.011 0.03 0.08 2.68 0.07 0.26 remainder 0.38 0.11 0.21 10.00 No. 139Example 17.12 13.88 0.57 0.024 0.09 0.10 2.51 0.12 0.34 remainder 0.900.19 0.33 7.92 No. 140 Example 16.66 11.58 1.02 0.057 0.11 0.04 2.740.12 0.22 remainder 2.75 0.51 0.15 2.63 No. 141 Example 16.21 13.21 0.320.044 0.08 0.12 2.15 0.79 0.41 remainder 0.67 0.20 0.63 4.55 No. 142Comparative 16.55 12.74 0.84 0.026 0.00 0.06 2.24 0.13 0.32 remainder0.00 0.06 0.07 2.31 Example No. 143 Comparative 17.25 12.79 0.74 0.0230.07 0.00 2.21 0.06 0.27 remainder — 0.07 0.09 3.04 Example No. 144Comparative 16.87 12.36 0.86 0.029 0.64 0.12 2.64 0.21 0.41 remainder5.33 0.76 0.88 26.21 Example No. 145 Comparative 16.39 13.11 0.71 0.0330.08 0.72 2.35 0.06 0.39 remainder 0.11 0.80 1.13 24.24 Example

In Table 19, among the sintered bodies of the respective sample Nos.,those corresponding to the invention are indicated by “Example”, andthose not corresponding to the invention are indicated by “ComparativeExample”.

Each sintered body contained very small amounts of impurities, but thedescription thereof in Table 19 is omitted.

10. Evaluation of Sintered Body (Y—Nb Based) 10.1 Evaluation of RelativeDensity

With respect to the sintered bodies of the respective sample Nos. shownin Table 19, the sintered density was measured in accordance with themethod for measuring the density of sintered metal materials specifiedin JIS Z 2501 (2000), and also the relative density of each sinteredbody was calculated with reference to the true density of the metalpowder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Table 20.

10.2 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shownin Table 19, the Vickers hardness was measured in accordance with theVickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 20.

10.3 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shownin Table 19, the tensile strength, 0.2% proof stress, and elongationwere measured in accordance with the metal material tensile test methodspecified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluatedaccording to the above-mentioned evaluation criteria applied to Tables 5and 8.

The evaluation results are shown in Table 20.

TABLE 20 Metal powder Evaluation results of sintered body Average par-Relative Vickers Tensile 0.2% proof Sample ticle diameter densityhardness strength stress Elongation No. — μm % — — — — No. 135 Example4.11 99.2 169 A A A No. 136 Example 3.89 99.1 170 A A A No. 137 Example3.94 99.0 172 A A A No. 138 Example 4.23 98.7 177 B A A No. 139 Example4.12 99.2 174 A A A No. 140 Example 3.87 98.5 180 B B B No. 141 Example3.69 98.4 181 B B B No. 142 Comparative 3.77 96.1 192 D D B Example No.143 Comparative 3.94 95.9 196 D D B Example No. 144 Comparative 4.7894.8 201 D E E Example No. 145 Comparative 4.56 94.6 204 D E E Example

As apparent from Table 20, it was confirmed that the sintered bodiescorresponding to Example each have a higher relative density than thesintered bodies corresponding to Comparative Example. It was alsoconfirmed that there is a significant difference in properties such astensile strength, 0.2% proof stress, and elongation between the sinteredbodies corresponding to Example and the sintered bodies corresponding toComparative Example.

11. Production of Sintered Body (V—Nb Based) Sample Nos. 146 to 155

Sintered bodies were obtained in the same manner as the method forproducing the sintered body of sample No. 1 except that the compositionand the like of the metal powder for powder metallurgy were changed asshown in Table 21, respectively.

TABLE 21 Metal powder for powder metallurgy Alloy composition E1 E2 E1 +(E1 + (E1 + Sample Cr Ni Si C (V) (Nb) Mo Mn O Fe E1/E2 E2 E2)/Si E2)/CRemarks No. — mass % — mass % — — — No. 146 Example 16.56 12.65 0.790.025 0.08 0.15 2.35 0.06 0.26 remainder 0.53 0.23 0.29 9.20 No. 147Example 16.42 12.36 0.71 0.016 0.05 0.10 2.28 0.09 0.31 remainder 0.500.15 0.21 9.38 No. 148 Example 17.23 12.15 0.89 0.022 0.15 0.21 2.230.07 0.68 remainder 1.25 0.27 0.30 12.27 No. 149 Example 17.89 11.750.97 0.047 0.09 0.09 2.59 0.05 0.18 remainder 1.00 0.18 0.19 3.83 No.150 Example 18.23 13.21 0.88 0.011 0.05 0.10 2.87 0.07 0.31 remainder0.50 0.15 0.17 13.64 No. 151 Example 18.25 10.25 0.44 0.187 0.12 0.122.47 0.07 0.47 remainder 1.00 0.24 0.55 1.28 No. 152 Comparative 16.5412.74 0.58 0.056 0.00 0.06 2.68 0.12 0.28 remainder 0.00 0.06 0.10 1.07Example No. 153 Comparative 16.39 12.47 0.75 0.032 0.09 0.00 2.13 0.110.32 remainder — 0.09 0.12 2.81 Example No. 154 Comparative 17.87 12.480.36 0.014 0.68 0.09 2.54 0.18 0.44 remainder 7.56 0.77 2.14 55.00Example No. 155 Comparative 17.65 12.77 0.47 0.023 0.07 0.63 2.77 0.160.39 remainder 0.11 0.70 1.49 30.43 Example

In Table 21, among the sintered bodies of the respective sample Nos.,those corresponding to the invention are indicated by “Example”, andthose not corresponding to the invention are indicated by “ComparativeExample”.

Each sintered body contained very small amounts of impurities, but thedescription thereof in Table 21 is omitted.

12. Evaluation of Sintered Body (V—Nb Based) 12.1 Evaluation of RelativeDensity

With respect to the sintered bodies of the respective sample Nos. shownin Table 21, the sintered density was measured in accordance with themethod for measuring the density of sintered metal materials specifiedin JIS Z 2501 (2000), and also the relative density of each sinteredbody was calculated with reference to the true density of the metalpowder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Table 22.

12.2 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shownin Table 21, the Vickers hardness was measured in accordance with theVickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 22.

12.3 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shownin Table 21, the tensile strength, 0.2% proof stress, and elongationwere measured in accordance with the metal material tensile test methodspecified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluatedaccording to the above-mentioned evaluation criteria applied to Tables 5and 8.

The evaluation results are shown in Table 22.

TABLE 22 Metal powder Evaluation results of sintered body Average par-Relative Vickers Tensile 0.2% proof Sample ticle diameter densityhardness strength stress Elongation No. — μm % — — — — No. 146 Example4.12 98.2 172 A A B No. 147 Example 4.25 99.0 167 A A A No. 148 Example6.89 98.5 175 A A B No. 149 Example 5.74 98.3 181 B B B No. 150 Example3.25 98.7 161 B B A No. 151 Example 4.11 97.4 194 B B C No. 152Comparative 3.98 96.2 202 D D C Example No. 153 Comparative 3.74 96.0211 D D C Example No. 154 Comparative 4.52 94.5 215 D D D Example No.155 Comparative 3.45 94.3 223 D D E Example

As apparent from Table 22, it was confirmed that the sintered bodiescorresponding to Example each have a higher relative density than thesintered bodies corresponding to Comparative Example. It was alsoconfirmed that there is a significant difference in properties such astensile strength, 0.2% proof stress, and elongation between the sinteredbodies corresponding to Example and the sintered bodies corresponding toComparative Example.

13. Production of Sintered Body (Ti—Zr Based) Sample Nos. 156 to 165

Sintered bodies were obtained in the same manner as the method forproducing the sintered body of sample No. 1 except that the compositionand the like of the metal powder for powder metallurgy were changed asshown in Table 23, respectively.

TABLE 23 Metal powder for powder metallurgy Alloy composition E1 E2 E1 +(E1 + (E1 + Sample Cr Ni Si C (Ti) (Zr) Mo Mn O Fe E1/E2 E2 E2)/Si E2)/CRemarks No. — mass % — mass % — — — No. 156 Example 16.85 12.74 0.860.023 0.06 0.12 2.54 0.07 0.31 remainder 0.50 0.18 0.21 7.83 No. 157Example 17.24 12.14 0.74 0.039 0.05 0.10 2.36 0.04 0.49 remainder 0.500.15 0.20 3.85 No. 158 Example 16.21 12.46 0.62 0.019 0.12 0.09 2.780.07 0.54 remainder 1.33 0.21 0.34 11.05 No. 159 Example 16.57 12.980.97 0.059 0.08 0.06 2.23 0.05 0.21 remainder 1.33 0.14 0.14 2.37 No.160 Example 17.85 12.41 0.88 0.009 0.05 0.10 2.74 0.07 0.35 remainder0.50 0.15 0.17 16.67 No. 161 Example 17.65 13.21 0.44 0.175 0.09 0.092.68 0.07 0.44 remainder 1.00 0.18 0.41 1.03 No. 162 Comparative 17.4412.47 0.72 0.055 0.00 0.06 2.75 0.18 0.26 remainder 0.00 0.06 0.08 1.09Example No. 163 Comparative 16.54 12.87 0.78 0.032 0.09 0.00 2.69 0.080.35 remainder — 0.09 0.12 2.81 Example No. 164 Comparative 16.32 13.580.38 0.021 0.64 0.08 2.41 0.07 0.28 remainder 8.00 0.72 1.89 34.29Example No. 165 Comparative 16.25 13.75 0.43 0.018 0.07 0.59 2.21 0.060.22 remainder 0.12 0.66 1.53 36.67 Example

In Table 23, among the sintered bodies of the respective sample Nos.,those corresponding to the invention are indicated by “Example”, andthose not corresponding to the invention are indicated by “ComparativeExample”.

Each sintered body contained very small amounts of impurities, but thedescription thereof in Table 23 is omitted.

14. Evaluation of Sintered Body (Ti—Zr Based) 14.1 Evaluation ofRelative Density

With respect to the sintered bodies of the respective sample Nos. shownin Table 23, the sintered density was measured in accordance with themethod for measuring the density of sintered metal materials specifiedin JIS Z 2501 (2000), and also the relative density of each sinteredbody was calculated with reference to the true density of the metalpowder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Table 24.

14.2 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shownin Table 23, the Vickers hardness was measured in accordance with theVickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 24.

14.3 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shownin Table 23, the tensile strength, 0.2% proof stress, and elongationwere measured in accordance with the metal material tensile test methodspecified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluatedaccording to the above-mentioned evaluation criteria applied to Tables 5and 8.

The evaluation results are shown in Table 24.

TABLE 24 Metal powder Evaluation results of sintered body Average par-Relative Vickers Tensile 0.2% proof Sample ticle diameter densityhardness strength stress Elongation No. — μm % — — — — No. 156 Example4.12 98.8 172 A A B No. 157 Example 4.25 99.0 167 A A A No. 158 Example5.87 98.6 184 A A B No. 159 Example 5.12 98.5 191 B B B No. 160 Example3.89 98.2 195 B B B No. 161 Example 4.47 97.4 199 B B C No. 162Comparative 4.11 96.3 205 D D C Example No. 163 Comparative 3.78 96.7211 D D C Example No. 164 Comparative 4.52 94.7 235 D D E Example No.165 Comparative 3.88 95.2 221 D D E Example

As apparent from Table 24, it was confirmed that the sintered bodiescorresponding to Example each have a higher relative density than thesintered bodies corresponding to Comparative Example. It was alsoconfirmed that there is a significant difference in properties such astensile strength, 0.2% proof stress, and elongation between the sinteredbodies corresponding to Example and the sintered bodies corresponding toComparative Example.

15. Production of Sintered Body (Zr—Ta Based) Sample Nos. 166 to 175

Sintered bodies were obtained in the same manner as the method forproducing the sintered body of sample No. 1 except that the compositionand the like of the metal powder for powder metallurgy were changed asshown in Table 25, respectively.

TABLE 25 Metal powder for powder metallurgy Alloy composition E1 E2 E1 +(E1 + (E1 + Sample Cr Ni Si C (Zr) (Ta) Mo Mn O Fe E1/E2 E2 E2)/Si E2)/CRemarks No. — mass % — mass % — — — No. 166 Example 16.61 12.45 0.680.023 0.06 0.09 2.55 0.11 0.38 remainder 0.67 0.15 0.22 6.52 No. 167Example 16.94 12.21 0.72 0.039 0.05 0.10 2.47 0.06 0.24 remainder 0.500.15 0.21 3.85 No. 168 Example 17.43 12.89 0.85 0.019 0.12 0.09 2.050.54 0.49 remainder 1.33 0.21 0.25 11.05 No. 169 Example 17.21 13.420.97 0.058 0.08 0.06 2.78 0.07 0.31 remainder 1.33 0.14 0.14 2.41 No.170 Example 16.31 12.87 0.88 0.011 0.05 0.10 2.74 0.12 0.55 remainder0.50 0.15 0.17 13.64 No. 171 Example 16.54 12.25 0.44 0.146 0.09 0.092.32 0.07 0.68 remainder 1.00 0.18 0.41 1.23 No. 172 Comparative 17.2412.14 0.72 0.018 0.00 0.06 2.56 0.08 0.27 remainder 0.00 0.06 0.08 3.33Example No. 173 Comparative 16.87 12.56 0.82 0.026 0.09 0.00 2.24 0.090.32 remainder — 0.09 0.11 3.46 Example No. 174 Comparative 16.54 12.320.35 0.025 0.78 0.05 2.89 0.11 0.35 remainder 15.60  0.83 2.37 33.20Example No. 175 Comparative 16.35 12.47 0.45 0.022 0.04 0.58 2.77 0.160.33 remainder 0.07 0.62 1.38 28.18 Example

In Table 25, among the sintered bodies of the respective sample Nos.,those corresponding to the invention are indicated by “Example”, andthose not corresponding to the invention are indicated by “ComparativeExample”.

Each sintered body contained very small amounts of impurities, but thedescription thereof in Table 25 is omitted.

16. Evaluation of Sintered Body (Zr—Ta Based) 16.1 Evaluation ofRelative Density

With respect to the sintered bodies of the respective sample Nos. shownin Table 25, the sintered density was measured in accordance with themethod for measuring the density of sintered metal materials specifiedin JIS Z 2501 (2000), and also the relative density of each sinteredbody was calculated with reference to the true density of the metalpowder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Table 26.

16.2 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shownin Table 25, the Vickers hardness was measured in accordance with theVickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 26.

16.3 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shownin Table 25, the tensile strength, 0.2% proof stress, and elongationwere measured in accordance with the metal material tensile test methodspecified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluatedaccording to the above-mentioned evaluation criteria applied to Tables 5and 8.

The evaluation results are shown in Table 26.

TABLE 26 Metal powder Evaluation results of sintered body Average par-Relative Vickers Tensile 0.2% proof Sample ticle diameter densityhardness strength stress Elongation No. — μm % — — — — No. 166 Example4.12 99.2 172 A A A No. 167 Example 4.32 99.3 167 A A A No. 168 Example5.74 98.7 181 A A B No. 169 Example 5.21 98.5 185 B B B No. 170 Example4.32 98.2 189 B B B No. 171 Example 4.23 97.5 197 B B C No. 172Comparative 3.88 96.2 199 D D C Example No. 173 Comparative 4.22 96.2199 D D C Example No. 174 Comparative 4.11 94.8 211 D D E Example No.175 Comparative 3.89 95.1 205 D D E Example

As apparent from Table 26, it was confirmed that the sintered bodiescorresponding to Example each have a higher relative density than thesintered bodies corresponding to Comparative Example. It was alsoconfirmed that there is a significant difference in properties such astensile strength, 0.2% proof stress, and elongation between the sinteredbodies corresponding to Example and the sintered bodies corresponding toComparative Example.

17. Production of Sintered Body (Zr—V Based) Sample Nos. 176 to 185

Sintered bodies were obtained in the same manner as the method forproducing the sintered body of sample No. 1 except that the compositionand the like of the metal powder for powder metallurgy were changed asshown in Table 27, respectively.

TABLE 27 Metal powder for powder metallurgy Alloy composition E1 E2 E1 +(E1 + (E1 + Sample Cr Ni Si C (Zr) (V) Mo Mn O Fe E1/E2 E2 E2)/Si E2)/CRemarks No. — mass % — mass % — — — No. 176 Example 16.58 12.47 0.750.022 0.09 0.06 2.36 0.08 0.31 remainder 1.50 0.15 0.20 6.82 No. 177Example 16.32 12.24 0.89 0.051 0.05 0.08 2.64 0.06 0.25 remainder 0.630.13 0.15 8.67 No. 178 Example 16.87 12.55 0.98 0.025 0.09 0.09 2.880.07 0.39 remainder 1.00 0.18 0.18 7.20 No. 179 Example 17.28 12.36 0.540.069 0.12 0.06 2.12 0.05 0.23 remainder 2.00 0.18 0.33 2.61 No. 180Example 17.59 12.98 0.88 0.012 0.08 0.08 2.58 0.02 0.45 remainder 1.000.16 0.18 13.33 No. 181 Example 17.25 12.78 0.44 0.118 0.09 0.09 2.680.07 0.61 remainder 1.00 0.18 0.41 1.53 No. 182 Comparative 16.34 12.630.77 0.054 0.00 0.06 2.84 0.08 0.36 remainder 0.00 0.06 0.08 1.11Example No. 183 Comparative 16.78 12.24 0.78 0.032 0.09 0.00 2.64 0.110.27 remainder — 0.09 0.12 2.81 Example No. 184 Comparative 16.24 12.360.38 0.021 0.61 0.08 2.31 0.09 0.18 remainder 7.63 0.69 1.82 32.86Example No. 185 Comparative 17.12 12.89 0.45 0.025 0.08 0.59 2.15 0.050.24 remainder 0.14 0.67 1.49 26.80 Example

In Table 27, among the sintered bodies of the respective sample Nos.,those corresponding to the invention are indicated by “Example”, andthose not corresponding to the invention are indicated by “ComparativeExample”.

Each sintered body contained very small amounts of impurities, but thedescription thereof in Table 27 is omitted.

18. Evaluation of Sintered Body (Zr—V Based) 18.1 Evaluation of RelativeDensity

With respect to the sintered bodies of the respective sample Nos. shownin Table 27, the sintered density was measured in accordance with themethod for measuring the density of sintered metal materials specifiedin JIS Z 2501 (2000), and also the relative density of each sinteredbody was calculated with reference to the true density of the metalpowder for powder metallurgy used for producing each sintered body.

The calculation results are shown in Table 28.

18.2 Evaluation of Vickers Hardness

With respect to the sintered bodies of the respective sample Nos. shownin Table 27, the Vickers hardness was measured in accordance with theVickers hardness test method specified in JIS Z 2244 (2009).

The measurement results are shown in Table 28.

18.3 Evaluation of Tensile Strength, 0.2% Proof Stress, and Elongation

With respect to the sintered bodies of the respective sample Nos. shownin Table 27, the tensile strength, 0.2% proof stress, and elongationwere measured in accordance with the metal material tensile test methodspecified in JIS Z 2241 (2011).

Then, the measured values of the physical properties were evaluatedaccording to the above-mentioned evaluation criteria applied to Tables 5and 8.

The evaluation results are shown in Table 28.

TABLE 28 Metal powder Evaluation results of sintered body Average par-Relative Vickers Tensile 0.2% proof Sample ticle diameter densityhardness strength stress Elongation No. — μm % — — — — No. 176 Example4.15 99.3 172 A A A No. 177 Example 4.26 98.9 167 A A B No. 178 Example5.74 99.0 180 A A B No. 179 Example 5.12 99.1 178 B B B No. 180 Example3.86 98.3 197 B B B No. 181 Example 3.65 97.5 202 B B C No. 182Comparative 4.05 96.2 209 D D C Example No. 183 Comparative 4.13 96.5208 D D C Example No. 184 Comparative 4.05 94.7 225 D D E Example No.185 Comparative 3.88 95.2 212 D D E Example

As apparent from Table 28, it was confirmed that the sintered bodiescorresponding to Example each have a higher relative density than thesintered bodies corresponding to Comparative Example. It was alsoconfirmed that there is a significant difference in properties such astensile strength, 0.2% proof stress, and elongation between the sinteredbodies corresponding to Example and the sintered bodies corresponding toComparative Example.

19. Evaluation of Specularity of Sintered Body 19.1 Evaluation ofPorosity Near Surface and Inside

First, each of the sintered bodies of the respective sample Nos. shownin Table 29 was cut and the cross section was polished.

Then, a porosity A1 near the surface of the sintered body and a porosityA2 inside the sintered body were calculated and also A2−A1 wascalculated.

The calculation results are shown in Table 29.

19.2 Evaluation of Specular Gloss

First, each of the sintered bodies of the respective sample Nos. shownin Table 29 was subjected to a barrel polishing treatment.

Then, the specular gloss of the sintered body was measured in accordancewith the method for measuring the specular gloss specified in JIS Z 8741(1997). The incident angle of light with respect to the surface of thesintered body was set to 60°, and as a reference plane for calculatingthe specular gloss, a glass having a specular gloss of 90 and arefractive index of 1.500 was used. Then, the measured specular glosswas evaluated according to the following evaluation criteria.

Evaluation Criteria for Specular Gloss

A: The specularity of the surface is very high (the specular gloss is200 or more).

B: The specularity of the surface is high (the specular gloss is 150 ormore and less than 200).

C: The specularity of the surface is slightly high (the specular glossis 100 or more and less than 150).

D: The specularity of the surface is slightly low (the specular gloss is60 or more and less than 100).

E: The specularity of the surface is low (the specular gloss is 30 ormore and less than 60).

F: The specularity of the surface is very low (the specular gloss isless than 30).

The evaluation results are shown in Table 29.

TABLE 29 Alloy Evaluation results Sample Example/ composition A2-A1Specular No. Comparative Example E1 E2 [%] gloss 2 Example Zr Nb 1.0 A23 Comparative Example 0.2 E 86 Example Hf Nb 0.9 A 95 ComparativeExample 0.2 E 116 Example Ti Nb 1.2 A 120 Comparative Example 0.1 E 126Example Nb Ta 0.6 C 131 Comparative Example 0.1 E 135 Example Y Nb 1.2 A142 Comparative Example 0.2 E 147 Example V Nb 0.6 C 152 ComparativeExample 0.1 E 157 Example Ti Zr 0.7 C 162 Comparative Example 0.1 E 167Example Zr Ta 0.6 B 172 Comparative Example 0.2 E 176 Example Zr V 0.5 B182 Comparative Example 0.2 E

As apparent from Table 29, it was confirmed that the sintered bodiescorresponding to Example each have a higher specular gloss than thesintered bodies corresponding to Comparative Example. This is consideredto be because the porosity near the surface of the sintered body issmall, and therefore, light scattering is suppressed, however, the ratioof regular reflection is increased.

What is claimed is:
 1. A metal powder for powder metallurgy, comprising:Fe as a principal component; Cr in a proportion of 15% by mass or moreand 26% by mass or less; Ni in a proportion of 7% by mass or more and22% by mass or less; Si in a proportion of 0.3% by mass or more and 1.2%by mass or less; and C in a proportion of 0.005% by mass or more and0.3% by mass or less, wherein when one element selected from the groupconsisting of Ti, V, Y, Zr, Nb, Hf, and Ta is defined as a firstelement, and one element selected from the group consisting of Ti, V, Y,Zr, Nb, Hf, and Ta, and having a larger group number in the periodictable than that of the first element or having the same group number inthe periodic table as that of the first element and a larger periodnumber in the periodic table than that of the first element is definedas a second element, the first element is contained in a proportion of0.01% by mass or more and 0.5% by mass or less, and the second elementis contained in a proportion of 0.01% by mass or more and 0.5% by massor less.
 2. The metal powder for powder metallurgy according to claim 1,wherein the metal powder has an austenite crystal structure.
 3. Themetal powder for powder metallurgy according to claim 1, wherein theratio (X1/X2) of a value (X1) obtained by dividing the content (E1) ofthe first element by the mass number of the first element to a value(X2) obtained by dividing the content (E2) of the second element by themass number of the second element is 0.3 or more and 3 or less.
 4. Themetal powder for powder metallurgy according to claim 1, wherein the sumof the content of the first element and the content of the secondelement is 0.05% by mass or more and 0.6% by mass or less.
 5. The metalpowder for powder metallurgy according to claim 1, further comprising Moin a proportion of 1% by mass or more and 5% by mass or less.
 6. Themetal powder for powder metallurgy according to claim 1, wherein themetal powder has an average particle diameter of 0.5 μm or more and 30μm or less.
 7. A compound, comprising the metal powder for powdermetallurgy according to claim 1 and a binder which binds the particlesof the metal powder for powder metallurgy to one another.
 8. A compound,comprising the metal powder for powder metallurgy according to claim 2and a binder which binds the particles of the metal powder for powdermetallurgy to one another.
 9. A compound, comprising the metal powderfor powder metallurgy according to claim 3 and a binder which binds theparticles of the metal powder for powder metallurgy to one another. 10.A compound, comprising the metal powder for powder metallurgy accordingto claim 4 and a binder which binds the particles of the metal powderfor powder metallurgy to one another.
 11. A compound, comprising themetal powder for powder metallurgy according to claim 5 and a binderwhich binds the particles of the metal powder for powder metallurgy toone another.
 12. A compound, comprising the metal powder for powdermetallurgy according to claim 6 and a binder which binds the particlesof the metal powder for powder metallurgy to one another.
 13. Agranulated powder, wherein the granulated powder is obtained bygranulating the metal powder for powder metallurgy according to claim 1.14. A granulated powder, wherein the granulated powder is obtained bygranulating the metal powder for powder metallurgy according to claim 2.15. A granulated powder, wherein the granulated powder is obtained bygranulating the metal powder for powder metallurgy according to claim 3.16. A granulated powder, wherein the granulated powder is obtained bygranulating the metal powder for powder metallurgy according to claim 4.17. A granulated powder, wherein the granulated powder is obtained bygranulating the metal powder for powder metallurgy according to claim 5.18. A granulated powder, wherein the granulated powder is obtained bygranulating the metal powder for powder metallurgy according to claim 6.19. A sintered body, wherein the sintered body is produced by sinteringa metal powder for powder metallurgy containing: Fe as a principalcomponent; Cr in a proportion of 15% by mass or more and 26% by mass orless; Ni in a proportion of 7% by mass or more and 22% by mass or less;Si in a proportion of 0.3% by mass or more and 1.2% by mass or less; andC in a proportion of 0.005% by mass or more and 0.3% by mass or less,and when one element selected from the group consisting of Ti, V, Y, Zr,Nb, Hf, and Ta is defined as a first element, and one element selectedfrom the group consisting of Ti, V, Y, Zr, Nb, Hf, and Ta, and having alarger group number in the periodic table than that of the first elementor having the same group number in the periodic table as that of thefirst element and a larger period number in the periodic table than thatof the first element is defined as a second element, the first elementis contained in a proportion of 0.01% by mass or more and 0.5% by massor less, and the second element is contained in a proportion of 0.01% bymass or more and 0.5% by mass or less.
 20. The sintered body accordingto claim 19, wherein the sintered body includes a first region which isin the form of a particle and has a relatively high silicon oxidecontent and a second region which has a relatively lower silicon oxidecontent than the first region.